Two posts ago I sent my props to Robin Harris (Storagemojo), now I’m feeling the bloggers biteback. Robin – what are you doing? . . .
My heartburn is with Robin for implying that Jon’s numbers might be relevant for enterprise storage and implying (by reference) that RAID is a problem too. Geez, Robin, you know better. I’m not even going to address the RAID thing because that is so wrong.
Server RAID is a problem
Never one to leave well enough alone, I have to respond to Marc: RAID is a problem. A problem that is getting worse every day. It is a problem for servers and it is a growing problem for enterprise IT.
Don’t get me wrong: RAID works for protecting data and improving storage performance. The problem is that the concept was developed almost 20 years ago and is showing its age.
Why RAID is a growing problem
There are three general problems with RAID:
RAID costs too much
Look at any mid-range or larger RAID array of 10 terabytes. It prices out, today, at about $80,000 to $120,000 or more. Call it $10k per terabyte. How much do the disks cost? Good quality SATA drives may be had for $500/TB. So the actual capacity of the array, only accounts for about 5% of the price. Use top of the line “enterprise” drives and it’s maybe 10%.
This is just silly. With cheap power and packaging and some front end RAM you could have three complete copies of all your data and lots of fast reads and writes for 25% of the cost.
Management is based on a broken concept
Why do we manage disks? We don’t manage main memory: virtual memory systems do that for us. With RAID, we don’t manage disks, we manage LUNs, which is a group of disks virtualized to look like a big disk. Useful, until you get to the point where you have as many LUNs as you once had disks. Now what?
Much of the popularity of NAS, IMHO, is because you manage files instead of disks and the data is network accessible.
Parity RAID is architecturally doomed
Vendors have made much of the limits of parity RAID – unless they didn’t have it to sell – because with the increase in disk capacity you are much more likely to encounter an uncorrectable read error during a rebuild. The answer: another costly disk. Good if you sell disks, less so if you buy them. But that’s the small problem.
The big problem with parity RAID is that I/O rates are flat as capacity rises. 20 years ago a 500 MB drive could do 50 I/O per second (IOPS), or 1 IOPS for every 10 megabytes of capacity. Today, a 150 GB, 15k drive, the ne plus ultra of disk technology, is at 1 IOPS for every 750 MB of capacity. Big SATA drives are at 1 IOPS per several gigabytes. And the trend is down.
With parity RAID, those precious IOPS get squandered on read/modify/write cycles. After a disk failure more get squandered rebuilding the data, effectively cutting that rank’s performance in half. This isn’t sustainable over the next decade.
The StorageMojo take
Yes, Marc, I do think server RAID is a problem. Not an omigawd-stop-buying-RAID problem – although some people have – but an oncoming train wreck that the industry needs to think about averting. In the 1980s DEC and IBM were very happy to make huge margins selling disk mirroring software. Then RAID came along and moved those margins into RAID controllers. Now RAID is coming to a crossroads. I suspect a new group of innovators will take the lead in the new paradigm.
BTW, be sure to check outEqualLogic products. A bunch of my readers really like them. One big plus: all software comes bundled with the system, so they don’t nickel and dime you to death. That’s pretty revolutionary itself.
Comments welcome. I’m off to NAB and Storage Networking World this week, so stay tuned for posts on more cool stuff.