Connecting Perl on UNIX or Linux to Microsoft SQL Server.Connecting Perl on UNIX or Linux to Microsoft SQL Server Perl DBIDBD ODBC Tutorial Part 3 This tutorial shows you how to access MS SQL Server databases from Perl on UNIX and Linux.Unix Microsoft Sql Server Jdbc Download FreeConnect Perl to SQL Server 2.SQL Server 2. 00.SQL Server 2. 00.SQL Server 2. 01.SQL Server 2. 01.SQL Server 2. 01.SQL Server Express.When developing this tutorial, we accessed SQL Server 2.Express databases from Perl on UNIX and Linux.Perl and Linux. To access SQL Server from Perl on Linux, we used Easysoft ODBC drivers with Perl DBI and DBD ODBC on Debian GNULinux, Red.Hat and Ubuntu Edgy Eft, Feisty Fawn, Gutsy Gibbon and Hardy Heron.Easysoft ODBC drivers should work with any recent 3.Linux distributionCent.OS, Fedora, Kubuntu, MandrakeMandriva, Open.SUSESUSE, Red. Hat Enterprise Linux RHEL, Slackware and so on.Pre requisites. The pre requisite software for this tutorial is Perl.We used Perl 5. 8, but you only need the minimum version required by the DBI and DBD ODBC modules, which is currently 5.Use perl version to see what version of Perl you have installed.DBI module. We used DBI 1.DBI 1. 6. 07, but the samples in this tutorial should work with anything after 1.To see if you have a recent enough version of DBI installed, run perl e use DBI 1.If you get an error like DBI version 1.DBI. If you get an error saying DBI cannot be found in INC, you have probably not got DBI installed.Go to CPAN to get an up to date version of the DBI module.DBD ODBCWe used DBD ODBC 1.DBD ODBC 1. 1. 7.You can use similar methods to the ones shown above to check whether DBD ODBC is installed and to see what version you have.To check that you have the DBD ODBC module installed perl e use DBD ODBC If you have not got DBD ODBC installed, see.Enabling ODBC support in Perl with Perl DBI and DBD ODBC for installation instructions.To show the DBD ODBC version perl MDBD ODBC e print DBD ODBC VERSION To show all drivers DBI knows about and their versions perl MDBI e DBI installedversions SQL Server ODBC driver.We used our UNIXLinux ODBC driver for SQL Server 7.Express to connect Perl to a remote SQL Server database Download the SQL Server ODBC driver for your Perl client platform.Registration required.FreeTDS is a set of libraries for Unix and Linux that allows your programs to natively talk to Microsoft SQL Server and Sybase databases.Technically speaking.Download JDBC Driver.Beginning in Microsoft JDBC Driver 4.SQL Server, an application can use the authenticationScheme connection property to indicate that it.Unix Microsoft Sql Server Jdbc Download' title='Unix Microsoft Sql Server Jdbc Download' />If the SQL Server ODBC driver is not currently available for your platform, check the list of ODBC ODBC Bridge Client platforms.The ODBC ODBC Bridge is an alternative SQL Server solution from Easysoft, which you can download from this site.Install and license the SQL Server ODBC driver on the machine where Perl is installed.For installation instructions, see the ODBC driver documentation.Refer to the documentation to see which environment variables you need to set LDLIBRARYPATH, LIBPATH, LDRUNPATH, SHLIBPATH depending on the driver, platform and linker.Unix Microsoft Sql Server Jdbc DownloadsIspirer MnMTK helps to convert Oracle to Microsoft SQL Server including database schema DDL, data and serverside business logic from Oracle to SQL Server.Filestream allows us to store and manage unstructured datain SQL Server more easily.Initially, the accounts of FILESTREAM assumed prodigious powers of concentration.Create an ODBC data source in etcodbc.SQL Server database you want to access from Perl.For example, this SQL Server ODBC data source connects to a SQL Server Express instance that serves the Northwind database.MSSQL Perl. Driver Easysoft ODBC SQL Server.Server mymachineSQLEXPRESS.User mydomainmyuser.Password mypassword.If the database you want to connect to is the default.SQL Server login, omit this attribute.Database Northwind.Use isql to test the new data source.For example. cd usrlocaleasysoftunix.ODBCbin. isql v MSSQL Perl.At the prompt, type help to display a list of tables.To exit, press return in an empty prompt line.Assumptions. Previous tutorials in this series This tutorial assumes you have read or understand all the concepts covered in the previous tutorials DBD ODBC Tutorial Part 1 Drivers, Data Sources and Connection and DBD ODBC Tutorial Part 2 Introduction to retrieving data from your database.Operating system.This tutorial was designed on UNIX and Linux, and we have assumed you are using UNIX or Linux too.However, all the Perl examples should work equally well on Windows so long as minor alterations for the command line are made.ODBC driver manager.We have assumed that you are using the unix.ODBC driver manager.All discussion in this document relating to the location and definition of ODBC data sources is for unix.ODBC. Accessing Microsoft SQL Server from Perl on UNIX or Linux.Testing Your Data Source The following script selects and fetches some test data.Use it to check that you can.Perl script. Remember to replace the data source.DBI Replace datasourcename with the name of your data source.Replace databaseusername and databasepassword with the SQL Server database username and password.ODBC datasourcename myuserqdatabaseusername mypasswordqdatabasepassword Connect to the data source and get a handle for that connection.DBI connectdatasource,user,passwordor die Cant connect to datasource DBI errstr This query generates a result set with one record in it.SELECT 1 AS testcol Prepare the statement.Cant prepare statement DBI errstr Execute the statement.Print the column name.NAME 0n Fetch and display the result set value.Disconnect the database from the database handle.Where to Go Now After you have tested your data source you are ready to start fetching and manipulating the data in your database from Perl.We suggest you take a look at DBD ODBC Tutorial Part 2 Introduction to retrieving data from your database or the excellent book Programming the Perl DBI, which you can find at http dbi.The rest of this tutorial concerns itself with MS SQL Server specific issues and common.MS SQL Server from Perl.Calling Procedures The following section shows you how to create and call SQL Server procedures that accept.To use the sample scripts in this section you need a SQL Server database in which you can.The data source that you specify in the scripts needs.Input Parameters Input parameters are used to supply values to a procedure.For example, a procedure that.SELECT statement might use an input parameter to supply a value in a WHERE clause.You provide input parameter values when the procedure is called.The following example script shows how to create a procedure that accepts one input.The procedure adds 1 to the input parameter value and returns the new value.The. script calls the procedure and displays the return value.DBI Replace datasourcename with the name of your data source.Replace databaseusername and databasepassword with the SQL Server database username and password.ODBC datasourcename myuserqdatabaseusername mypasswordqdatabasepassword mydbh DBI connectdatasource,user,passwordor die Cant connect to datasource DBI errstr This procedure takes one input parameter.It adds 1 to the input parameter value and returns the new value.CREATE PROCEDURE PROCRETURNINPUTPARAM inputval int AS SET inputval inputval1 RETURN inputval The first placeholder in this prepared statement is used to capture the return value of the called procedure.The second placeholder represents the value thats supplied as the procedures input parameter.PROCRETURNINPUTPARAM myoutput myi1 Bind value for the first placeholder.Because the prepared statement updates the bind value, bindparaminout rather than bindparam needs to be used.Bind value for second placeholder.This is value for the procedures input parameter.Execute the prepared statement.Output the procedures return value.DROP PROCEDURE PROCRETURNINPUTPARAM dbh disconnect This example script inserts rows into a table with an identity column and uses IDENTITY to.The identity value is a unique, incremental.SQL Server automatically generates when a new row is added to the table.The procedure in the script accepts one input parameter a value to insert into the new row.The procedure returns the rows identity value. Descargar Juegos Gratis Para Psp Go 2010 Ford . DBI Replace datasourcename with the name of your data source.Replace databaseusername and databasepassword with the SQL Server database username and password.
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Use a jigsaw to cut out shapes for windows, and use a drill with a carbide grit hole saw to drill out holes for pipes. Install the sheet 18 inch above the first, leaving room for thinset mortar, which will strengthen the seam. How To Install Backer BoardUse 18 inch spacers to maintain the gap as you secure the board with the cement board screws. Cut the boards for the remaining sides of the tub and install them in the same manner, leaving 18 inch gaps in between adjacent boards. Cover each of the seams with fiberglass mesh tape. Smooth the tape along the seams, keeping it centered on either side of the joint, and cut off the excess when you reach the end. Prepare a batch of thinset mortar according to the manufacturers instructions. It should resemble a thick paste when youre finished. Spread a layer of the thinset mortar on the taped seams with a metal putty knife. As you spread on the mortar, press it through the tape and into the space between the boards. 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DJI Will Turn Off Your Spark Drone if You Dont Update Firmware by September 1st. Chinese manufacturer DJI has announced that owners of its Spark drone have until September 1st to update their firmware to the latest version or be totally locked out. Per Quartz, the decision to essentially hold users devices hostage came after reports of the drones randomly falling out of the sky, which users think was due to an issue with Sparks battery firmware. In a press release, the company suggested it took the hardline approach due to safety concerns. DJI decided on the option of a mandatory firmware update in order to maximize flight safety and product reliability which we consider as top priorities, the company wrote. The update will improve stability, connectivity and the battery firmware. While locking users out of their software is questionable, its indisputable that nobody wants a blade spinning drone to come crashing down on their heads. That goes double for a manufacturer which could, in theory, be held liable for a major safety issue. Locking users out is a dramatic measure. But the press release does not rule out the possibility of updating the software after the deadline to return their Sparks to flight ready status. In the unlikely possibility there is no official ability to install the new update after the deadline, its nearly certain the drone community would come up with some kind of way to unofficially update it to the correct version and restore normal functionality. In May, DJI also announced users would be locked out of flight capabilities if they failed to register their devices in its databaseensuring software updates would allow users to comply with regional regulations. The good news As Gizmodo noted in its review of the Spark, the drone itself is awesome, packing the feature set of a much larger drone into a small and capable package. MARINE ENGINES PROPULSION. Ranger Hope 2015. 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Female to 3. 5 mm Male stereo audio cable 3 mMicro USB to USB cable. Apple in ear Headphones. Lightning to USB cable. Binder clip. Eye maski. Pad mini 4. Pack. Towl Original SMac. Book Pro Retina 1. Umbrella. Clipboard A4 size4 pens, erasercheero mobile battery 1. AhCard case. Mouse. Male to 3. 5 mm Male stereo audio cable 5. Micro USB to Lightning converter. Male to 3. 5 mm Female stereo audio plug converter. Stamp. Moleskine. Cloth for glasses. Tissues. Flushable wet tissue. Flushable tissue. Surgical Mask. OCW T4. TD 1. AJF watch. Wallet. Hand towel. Keys,USB micro. SD readerwriter with micro. SDWhistlei. Phone. Suica. We know youve got a cool bag with some smart ideas inside, so let us knowShare your bag in our Lifehacker Go Bag Show and Tell Flickr pool, shoot me a message through the link below, or post it to your own Kinja blog with the tag featured bag. The photo has to be at least 8. Why Apples i. Phone 7 Headphones Dont Work on the Latest Mac. Book. Recently, a new staff member started at Lifehacker. She booted up her brand new, company issued Mac. Book Pro, and went to plug in her Ear. Pods to listen to some tunes while she worked. She was met with the same baffling conundrum as other Apple die hards who rush to procure the latest release Why the hell cant you use the i. Phone 7s Lightning connector headphones with the new Mac. Book Pro Why Get Lightning Headphones in the First Place First, some background. In 2. 01. 2, Apple introduced the smaller Lightning port on the i. Phone 5 replacing the 3. While the Lightning port necessitated a new charging cable, the Lightning connector was more compact than its predecessor and one could plug it into i. OS devices in either direction, making it more convenient. With the i. Phone 7, Apple made the courageous decision to force the use of its Lightning compatible Ear. Pod headphones by removing the 3. In short, your 3. Ear. Pods that came with the phone, you bought a new pair of Lightning headphones, or you went wireless with Bluetooth compatible headphones to listen to music. Using your old 3. Phone 7 is still possible, but requires the 3. Lightning adapter that comes included with the new i. Phone. That meant carrying around an extra, easy to lose little piece of equipment. Its an example of Apple making design decisions that impact function for the sake of form, a decision the companys made at many points in its past for example, its decision to remove the optical drive in its 2. Macs. I admit, I get a wee bit frustrated when trying to remember which cord goes in which slot for allRead more Read. Removing the 3. 5mm headphone jack was was a positive change, by some metrics. By routing audio through the Lightning port, the phone can play higher quality, 2. Headphone manufacturers are also taking advantage of the fact that headphones can draw power from the i. Phones Lightning port, adding features like noise cancellation and interference reducing DACs digital to analog converters to improve sound quality. But Lightning only headphones only work on i. OS devices with Lightning ports. To listen to music on anything else, like your computer, or even an older i. Phone, youll need to tote around another pair of headphones. There Are No Functional Adapters Yet. Naturally, you might think theres some sort of workaround, or an adapter that can easily fix this incompatibility issue. After all, Apple makes its own adapters for a variety of older interfaces for instance, VGA port adapters for mirroring your i. OS device on a monitor. But unlike 3. 5mm headphones, which can be used with an i. Phone 7 via the Apple made dongle, theres no way to do the reverse and get Lightning headphones to work with anything that doesnt have a Lightning port, making my colleagues new Mac. Book Pro, with its four high speed, reversible USB C ports and single 3. We hate to break it to you, but the traditional USB ports youve used to connect your cameras,Read more Read. A dongle does exist to plug Lightning port headphones into a USB C port, and we tried one, but it still didnt fix the problem. Lightning to USB C adapters only work when charging or transferring data. Which means no audio support, which means no Ear. Pod powered desk concerts in your open plan office. Apple Is Comfortable With User Hostile Tech. Apples Lightning connector is convenient for Apple, but not so much for the rest of us. Its only available on Apples i. OS devices, making switching to, say, an Android device an inconvenient and pricey decisionyoull need new cables, headphones, docks etc. To play nice with others, Apple should have either left the 3. Phone, or switched to USB C, which is what every other cell phone manufacturer is doing. And while their move towards incompatibility with other companys devices isnt surprising, it does seem a little weird that theyd build this kind of glaring incompatibility into their two most recent devicesthe i. Phone 7 and the latest Mac. Book pro. The decision to exclude the Lightning port from its Macsand not to publicly address the compatibility issues also runs counter to its history of transition tools. During the companys switch from Power. PC to Intel processors, it released the Rosetta translator software to keep Power. PC apps running on Intel powered Macs. When the Mac. Book Air debuted without an optical drive, the companys external Super. Drive optical drive eased the transition. My theory The removal of the headphone jack and inclusion of Lightning Ear. Pods is simply a stop gap to the companys true goal of forcing you to go wireless and buy Air. Pods or Beats Bluetooth headphones. Considering the options, going wireless might be the answer, though Id rather get some headphones that, you know, sound good. Ensure critical data is protected and available with the most widely deployed RAID data protection architecture. Our broad range of MegaRAID controller cards. I think the title says it all but here are some details I have a hardware RAID setup. Machine is AMD 6core with MSI 890FXA motherboard. I have two hard drives of 1TB. Genuine, refurbished Dell K869T iDRAC6 Enterprise Remote Access Controller for R T Series Servers. Removed from a working PowerEdge R610 Server. Compare Hardware Raid Software Raid Controller ErrorsRAID Levels Spans, Stripes, IOPS, Oh My Posted By Jon on Aug 4, 2. Youre probably familiar with the different standard RAID levels 1, 5, 1. RAID level has on the same hardware set. Ive always searched and found benchmarks of hardware similar to what I was looking for, but it was always hard to find the same exact hardware configured and benchmarked in different configurations. So, I decided I would do some testing myself to quantify the performance differences between configurations to help determine what I should run at the end of the day. Whenever someone asks what type of RAID they should run the answers are always RAID 1. RAID 5 for space and RAID 1 if you dont have more than 2 disks. Well, is that true Is RAID 1. 0 truly faster than a RAID 5Hardware Used for Testing. For this test, I used a Dell R7. PERC6i controller. The server is equipped with two Intel Xeon E5. GB of RAM. I also gathered 8 DellHP 2. SAS 1. 46. GB 1. 0K RPM disks. The server is running ESXi 6. USB thumb drive and Ive installed OMSA within ESXi so that I can reconfigure the RAID throughout the test without having to enter the RAID controller at boot. When configuring different levels of RAID you might notice a setting called Disks per span. Disks per span is the number of disks that are included in the subset of the RAID configuration. Since we know that a RAID 5 configuration is just one set of disks, there is no disks per span to configure if you have 8 disks and select all of them to be in the VD Virtual Disk then you have 8 disks in the array with zero hot spares. RAID 1. 0, however, is comprised of multiple RAID 1s striped rightHi, Two questions. My DL380 Gen8 server is equipped with a 1GB HP Smart Array RAID Controller P420i. Whats the difference between the P420 and P420i Any. So, if you have 8 disks in RAID 1. Obviously with the former you will have 4 spans of 2 disks each. If you do the latter, youll have 2 spans of 4 disks each. RAID 5. 0 is just a striped set of RAID 5 configurations. With 8 disks you really only have two options you can use 3 disks per span or 4 disks per span however, if you only use 3 disks per span then youll end up having 2 unused drives in the array which you could configure for hot spares. In order to find out which of these configurations offers the best performance you guessed it, were going to build each, let it fully initialize, create a datastore on it, v. Motionsv. Motion a VM to the datastore, and run the test. For the test Ill be using the Crystal Disk. Mark. I will be running the test as follows 3 times, and then averaging the results Crystal Disk. Mark Settings. I will be running the test as mentioned above RAID 5 with all disks, RAID 1. RAID 1. 0 with 4 disks per span, RAID 5. All tests are using Write back Cache and 6. A later test will be to play with the stripe size and see what yields the best performance into the virtual environment, but that will come later. The results, averaged, for each test are below RAID 5 with all disks 6. RAID 5 all disks. Avg MBs. Avg IOPSSequential Read Q 3. T 1 4. 90. Sequential Write Q 3. T 1 2. 73. Random Read 4. Ki. B Q 3. 2,T 1 1. Random Write 4. Ki. B Q 3. 2,T 1 5. Sequential Read T 1 2. Sequential Write T 1 2. Random Read 4. Ki. B Q 1,T 1 2. Random Write 4. Ki. B Q 1,T 1 4. RAID 1. 0 with 2 disks per span 6. RAID 1. 0 2 disks per span. Avg MBs. Avg IOPSSequential Read Q 3. T 1 3. 78. Sequential Write Q 3. T 1 2. 84. Random Read 4. Ki. B Q 3. 2,T 1 1. Random Write 4. Ki. B Q 3. 2,T 1 1. Sequential Read T 1 2. Sequential Write T 1 2. Random Read 4. Ki. B Q 1,T 1 1. Random Write 4. Ki. B Q 1,T 1 1. RAID 1. 0 with 4 disks per span 6. RAID 1. 0 4 disks per span Avg MBs Avg IOPSSequential Read Q 3. T 1 3. 94. Sequential Write Q 3. T 1 2. 11. Random Read 4. Ki. B Q 3. 2,T 1 1. Random Write 4. Ki. B Q 3. 2,T 1 1. Sequential Read T 1 2. Sequential Write T 1 2. Random Read 4. Ki. B Q 1,T 1 1. Random Write 4. Ki. B Q 1,T 1 9. RAID 5. 0 with 4 disks per span 6. RAID 5. 0 4 disks per span Avg MBs Avg IOPS Sequential Read Q 3. T 1 3. 41. Sequential Write Q 3. T 1 2. 59. Random Read 4. Ki. B Q 3. 2,T 1 1. Random Write 4. Ki. B Q 3. 2,T 1 5. Sequential Read T 1 1. Sequential Write T 1 2. Random Read 4. Ki. B Q 1,T 1 1. Random Write 4. Ki. B Q 1,T 1 4. Keep the figures above in mind as you read the charts below. Understand that queue depth is an important thing to consider when looking at throughput MBs and IOPS. With that said, the below graphs compare each array configuration to one another in the same test manner. This is where the configurations will start to stand out from one another. Above youll find that a RAID 5 with the 8 drives in it will outperform every other configuration in the sequential read test with a queue depth of 3. Not surprising, the only array configuration that struggles in the sequential write with a queue depth of 3. RAID 1. 0 with 4 disks per span. This is because the RAID 1. RAID 1s with 4 disks in each group. This slows down performance as youre really not able to reap the benefits of RAID 0 in this configuration since you only have one striped set. Above you will find that in a random read test the RAID 5 and 5. The RAID 5 wins because it has 8 disks assisting in read speed vs. RAID 1. 0s having fewer in striped configurations. RAID 5. 0 does almost as well as RAID 5 because it has 4 disk assisting in the read but is striped across two spans. So, dont discount RAID 5 or 5. Now things start to get interesting What you see here is more like what you would expect based on RAID configuration reputation you may read about. Note that the RAID 5 and RAID 5. Notice, though, that the RAID 1. RAID 5 and 5. 0. These write tests are skewed by the write back cache in the controller but the data still needs to leave the cache and be written to the disks, so the test is valid. The cache on a PERC6i is not huge though its usually only 2. MB 5. 12. MB of DDR2. Considering were doing 1,0. MB tests we unload the cache to disk several times during the process. So, what does all of this mean To me, it means three things You need to know what your workload will be in order to choose a configuration. You need to know what the ideal disks per span is for your configuration and total number of disks as the RAID 1. Finally, RAID 55. I can hear the gasps now but its true. If you have a setup that relies heavily on deep queue reads like copying large files for video editing, etc. and you care most about peak throughput then RAID 5 is your best choice. This also works to your advantage in that RAID 5 is the least wasteful configuration in terms of disk space. There are caveats to building RAID 55. However, if you are building storage for a VM setup or database then there are better options. We all know that RAID 1. RAID 1. 0 really wins in any application where IOPS are preferred in general VM storage included. Now, an 8 disk RAID 1. IOPS but it sure is better than a RAID 5 or RAID 5. And, imagine if there were 8 SSDs in the array instead of spinning disks. If youre wondering what Jon. Kensy. com runs on its not a straightforward answer. I use 8 Western Digital 4. TB Red drives in a RAID 5. LSI 9. 26. 0 8i controller as my primary storage in my main VMware ESXi host. The reason I went RAID 5. I wanted as much storage as possible while offering me some hope of rebuilding the array should a disk fail, while also performing well. I have two spans of 4 disks which is still a pretty large disk size but it kept my span size small so hopefully I can rebuild a failed drive in one half of the RAID 5. But, to complicate matters, I use SSD caching within VMware to enhance read performance of frequently used hot data. VMware Virtual Read Flash Cache operates at a per VM level, though. So, most of this website will be served up at SSD speeds because the database is utilizing that SSD Virtual Read Cache. And, to further complicate matters, I do have a dedicated SSD within the ESXi host that serves up VMs that do not need any redundancy but do need as many IOPS as possible. An example of a server that runs off of that dedicated SSD is my terminal server I have 1 4 users on it any given time which benefits greatly from IOPS. There are further settings that can be tweaked within a RAID configuration, like strip size 6. When No Redundancy Is More Reliable The Myth of Redundancy. Risk in a difficult concept and it requires a lot of training, thought and analysis to properly assess given scenarios. Often, because risk assessments are so difficult, we substitute risk analysis with simply adding basic redundancy and assuming that we have appropriately mitigated risk. But very often this is not the case. The introduction of complexity or additional failure modes often accompany the addition of redundancy and these new forms of failure have the potential to add more risk than the added redundancy removes. Storage systems are especially prone to these decision processes which is unfortunate as few, if any, systems are so susceptible to failure and more important to protect. RAID is a great example of where a lack of holistic risk thinking can lead to some strange decision making. If we look at a not uncommon scenario we will see where the goal of protecting against drive failure can actually lead to an increase in risk even when additional redundancy is applied. In this scenario we will compare a twelve drive array consisting of twelve three terabyte SATA hard drives in a single array. It is not uncommon to hear of people choosing RAID 5 for this scenario to get maximum capacity and performance while having adequate protection against failure. The idea here is that RAID 5 protects against the loss of a single drive which can be replaced and the array will rebuild itself before a second drive fails. That is great in theory, but the real risks of an array of this size, thirty six terabytes of drive capacity, come not from multiple drive failures as people generally suspect but from an inability to reliably rebuild the array after a single drive failure or from a failure of the array itself with no individual drives failing. The risk of a second drive failing is low, not non existent, but quite low. Drives today are highly reliable. Once one drives fails it does increase the likelihood of a second drive failing, which is well documented, but I dont want this risk to mislead us from looking at the true risks the risk of a failed resilvering operation. What happens that scares us during a RAID 5 resilver operation is that an unrecoverable read error URE can occur. When it does the resilver operation halts and the array is left in a useless state all data on the array is lost. On common SATA drives the rate of URE is 1. That means that a six terabyte array being resilvered has a roughly fifty percent chance of hitting a URE and failing. Fifty percent chance of failure is insanely high. Imagine if your car had a fifty percent chance of the wheels falling off every time that you drove it. So with a small by todays standards six terabyte RAID 5 array using 1. URE SATA drives, if we were to lose a single drive, we have only a fifty percent chance that the array will recover assuming the drive is replaced immediately. That doesnt include the risk of a second drive failing, only the risk of a URE failure. It also assumes that the drive is completely idle other than the resilver operation. If the drives are busily being used for other tasks at the same time then the chances of something bad happening, either a URE or a second drive failure, begin to increase dramatically. With a twelve terabyte array the chances of complete data loss during a resilver operation begin to approach one hundred percent meaning that RAID 5 has no functionality whatsoever in that case. There is always a chance of survival, but it is very low. At six terabytes you can compare a resilver operation to a game of Russian roulette with one bullet and six chambers and you have to pull the trigger three times. With twelve terabytes you have to pull it six times Those are not good odds. But we are not talking about a twelve terabyte array. We are talking about a thirty six terabyte array which sounds large but this is a size that someone could easily have at home today, let alone in a business. Every major server manufacturer, as well as nearly all low cost storage vendors, make sub 1. Resilvering a RAID 5 array with a single drive failure on a thirty six terabyte array is like playing Russian roulette, one bullet, six chambers and pulling the trigger eighteen times Your data doesnt stand much of a chance. Add to that the incredible amount of time needed to resilver an array of that size and the risk of a second disk failing during that resilver window starts to become a rather significant threat. Ive seen estimates of resilver times climbing into weeks or months on some systems. That is a long time to run without being able to lose another drive. When we are talking hours or days the risks are pretty low, but still present. When we are talking weeks or months of continuous abuse, as resilver operations are extremely drive intensive, the failure rates climb dramatically. With an array of this size we can effectively assume that the loss of a single drive means the loss of the complete array leaving us with no drive failure protection at all. Now if we look at a drive of the same or better performance with the same or better capacity under RAID 0, which also has no protection against drive loss, we need only use eleven of the same drives that we needed twelve of for our RAID 5 array. What this means is that instead of twelve hard drives, each of which has a roughly three percent chance of annual failure, we have only eleven. That alone makes our RAID 0 array more reliable as there are fewer drives to fail. Not only do we have fewer drives but there is no need to write the parity block nor skip parity blocks when reading back lowering, ever so slightly, the mechanical wear and tear on the RAID 0 array for the same utilization giving it a very slight additional reliability edge. The RAID 0 array of eleven drives will be identical in capacity to the twelve drive RAID 5 array but will have slightly better throughput and latency. A win all around. Plus the cost savings of not needing an additional drive. So what we see here is that in large arrays large in capacity, not in spindle count that RAID 0 actually passes RAID 5 in certain scenarios. When using common SATA drives this happens at capacities experienced even by power users at home and by many small businesses. If we move to enterprise SATA drives or SAS drives then the capacity number where this occurs becomes very high and is not a concern today but will be in just a few years when drive capacities get larger still. But this highlights how dangerous RAID 5 is in the sizes that we see today. Everyone understands the incredible risks of RAID 0 but it can be difficult to put into perspective that RAID 5s issues are so extreme that it might actually be less reliable than RAID 0. That RAID 5 might be less reliable than RAID 0 in an array of this size based on resilver operations alone is just the beginning. In a massive array like this the resilver time can take so long and exact such a toll on the drives that second drive failure starts to become a measurable risk as well. And then there are additional risks caused by array controller errors that can utilize resilver algorithms to destroy an entire array even when no drive failure has occurred. As RAID 0 or RAID 1 or RAID 1. These are hard risks to quantify but what is important is that they are additional risks that accumulate when using a more complex system when a simpler system, without the redundancy, was more reliable from the outset. Now that we have established that RAID 5 can be less reliable than RAID 0 I will point out the obvious dangers of RAID 0. RAID in general is used to mitigate the risk of a single, lone hard drive failing. We all fear a single drive simply failing and all data being lost. RAID 0, being a large stripe of drives without any form of redundancy, takes the risk of data loss of a single drive failing and multiplies it across a number of drives where any drive failing causes total loss of data to all drives. So in our eleven disk example above, if any of the eleven disks fails all is lost. It is clear to see where this is dramatically more dangerous than just using a single drive, all alone. What I am trying to point out here is that redundancy does not mean reliability. Just because something is redundant, like RAID 5, provides no guarantee that it will always be more reliable than something that is not redundant. |
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November 2017
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