Storage experts: Does size matter?
Hard drives, large and small
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You The Expert There has been much ado about 2.5-inch, small form-factor (SFF) hard disk drives of late and how they are better than the larger 3.5-inch drives. Does size matter?
Several storage array vendors have started using SFF drives in their arrays. The VSP from Hitachi Data Systems is one such drive. HP has OEMed this from HDS's parent Hitachi as its P9500. IBM's Storwise V7000 and DS8800 arrays are also SFF fans. NetApp has adopted 2.5-inch drives in its latest FAS arrays, and Compellent has added extra support for SFF drives in it latest Storage Center array.
Are SFF drives really better than 3.5-inch drives? For sure, SFF drives need less power to spin and there can be more of them in a drive tray meaning you can spread data across more spindles and get better I/O rates. But drives are mechanical and they break. So the more there are in an enclosure or rack the greater the probability of a drive failing and its data needing recovery or re-building.
Also the increased I/O you get from more spindles is a small improvement compared to the much faster I/O you can obtain from solid state drives (SSDs) which, since they are solid state and not mechanical, are less prone to error and failure.
SSDs are more expensive gigabyte for gigabyte, so SFF drives can provide a better balance of affordability, capacity and performance. Perhaps the ideal array at present is one with SSDs for the small core of hot data, SFF drives for less highly active data which is present in larger amounts, and traditional 3.5-inch drives for storing the bulk data which has low access rates but still does need to be directly online.
A countervailing view is that multi-level cell flash holds more data for less money than the faster single-level cell flash. This would mean therefore, that you only need two tiers of storage in an array – SSD and traditional 3.5-inch drives – with no place for the 2.5-inch drives and no need for them. They are a stopgap, that's all.
Does size matter? We have asked some reader-experts what they think about the issue and we'll publish their thoughts on low-power and small versus larger, higher capacity drives later this week. ®
COMMENTS
Huh?
I'm sorry but I fail to see the point of this article. (Hence the flame for El Reg. Sorry El Reg.)
3.5" vs 2.5" form factor? Hmmm let me think...
The benefit of a 3.5" disk is density per drive. That is that I can get a cheap 2 TB drive (3TB drives are popping up.) So for systems where I'm limited by the number of drives per box, and I don't care about the number of spindles ... 3.5" SATA drives make sense. (Read: More $$$ per TB when you buy 2.5" drives.)
Then the author points out... SSDs are the fastest thing out there. Funny how they fit them in to 2.5" drive devices. But then the author points out the obvious. SSDs are *expensive* and on a large scale, they are cost prohibitive.
No Duh.
So what's a drive array maker to do? Hmmm. Combine 2.5" hard drives, and 2.5" SSDs in the same chassis? Wow! Simply Brilliant. Definitely worth writing an article on... Take two devices that have the same form factor and put them in the same drive array so we can offer limited fast storage for the hot stuff and cheaper (slower) access for the rest of the kit.
For database stuff, its RAID 10 not RAID 5 so if a drive fails, you pop one out, and put a new one in. Its not as 'costly' to repair a raid 10 disk failure as it is to repair raid 5. ;-)
So I have to ask... how much was the El Reg reporter paid to write a fluff piece on storage arrays? Not from El Reg, but Hitachi?
Sorry El Reg, boring and bad writing.
But what do I know? Its not like I support Database systems that use large arrays. Or clusters of 'commodity' hardware in Hadoop/Hbase environments? Oh wait I do....
Same arguments back in the 5.25" vs. 3.5" days...
And with the same result. 3.5" drives will be pretty scarce in a few years, not just in storage arrays but in PCs you buy and in consumer electronics. 2.5" drives take up less volume per gigabyte and use less power per gigabyte, and those are the only figures of merit that matter anymore for rotating media.
IOPS in rotating media are now pretty much irrelevant in the face of the orders of magnitude increase you get from SSDs, versus the tiny gains you get from spinning faster, using more power to get faster seeks, or using more efficient interfaces like SAS or FC.
I expect by the next generation of arrays we'll see only two types of storage, SSDs for the obvious I/O benefits, and 2.5" SATA drives for bulk storage. SAS and FC interfaces will disappear. 7200 rpm will be as fast as it gets, and I wouldn't be surprised if we don't even step back to 5400 rpm to get slightly better density and power characteristics. After all, all that hot data is going be living on the SSDs.
WD drives.
Say what you want about Western Digital drives in general - and I've no good words for the Velociraptors - but I'll be damned if the RE4 Green Power 2TB drives aren't solid gear. Slow as sin...but they store a great many bits very reliably.
Bad (terrible!) idea as primary storage. Not remotely half bad as archival storage or in a MAID.
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