John Galea's Blog

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All things storage

I’ve recently had a hard drive failure, something which all of us at one time or another will endure. The issue these days is the large drives hold a lot of stuff so the loss you suffer is getting bigger and bigger. I’ve always kept my most important stuff on a mirrored drive but the rest of my stuff has remained vulnerable. So this time I decided it was time to relook at how I lay this out. I am restricted by the number of SATA ports in my system to 4 so this itself imparts a limitation on what I can consider in options.

I used a hardware RAID card for a little bit and a number of systems have BIOS supported RAID but what concerns me about that is if the card or motherboard dies then you loose your raid array entirely.

Microsoft have software based RAID but it is only available in there server OSs. The software RAID works well, is reliable and because it’s built in to the OS you can take the drive into another system should your entire system die. I recently explored the RAID 5 options and wanted to see what it can do and what it’s limitations are. I am using Server 2008 R2. The RAID 5 implementation is quite limited. It means you need to plan ahead. You can not increase the size of the drives in the array and expand the space. You can not add additional drives in the future (for example go from 3 to 4 drives). So all this means you need to plan ahead. I created a 3 drive RAID 5 array based on 2 TB drives. Initial sync took over 40 hours to complete. My good friend Sean commented that storage vendors recommend a min of RAID 6 if using SATA drives for this very reason. RAID 6 can handle a double drive failure and the chance of a failure while trying to rebuild after a drive failure could be hastened by rebuilding the array for 40 hours! I also discovered after a power hit it had to resync the whole drive so there went another 40 hours. Most good RAID needs only to resync some of the drive. This becomes problematic quickly.

I work on Virtual machines running under VMware. I’ve learned a number of things of late in this category too … RAID 5 created arrays can not use thin provisioning. When the array is sync’d it immediately writes to the entire size of the drive. I have been using Raw data mapping under VMware. One of the nice features of this is you can take the drive out of the VMware box and put it in a native Windows box. Really quite slick.

iSCSI is a more efficient (faster than file shares) way of using the network to host files like VMs for example. VMware supports iSCSI. A little while ago Microsoft finally added a download for iSCSI for 2008R2 for iSCSI target (read server)! Server 2012 includes this built in. Nice, this provides some nice options not previously available. I played a little bit with the 2012 implementation. It fully supports clustering of the iSCSI. The LUN is stored on the server as a file. It unfortunately does not support thin provisioning. You can however increase the size of the drive. But I don’t see a way to shrink it. It does support snapshotting of the LUN. There is no ability to mount a physical drive with iSCSI. If you want to read more about MS iSCSI checkout this article.. I found a few inexpensive consumer grade NAS two bay devices that support iSCSI. This is uncommon to say the least. It would include the IOMEGA X2, QNAP TS-212, and the Synology DS212j.

Almost all drives today support SMART which is a mechanism for drives to report their health. Windows chooses to not implement anything that might pay attention to this leaving the end user waiting for a drive to fail. There are tools to help out with this. The best one I found was Disk Checkup which includes the ability to inform you by message or email of an impending drive failure. It can even run self tests and the like.

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October 24, 2012 - Posted by | Uncategorized

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