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According to this IBM page,

RAID level-x0 allows more physical drives in an array. The benefits of doing so are larger logical drives, increased performance, and increased reliability.

So say, instead of having a single RAID 0 array with four drives, you could span two RAID 0 arrays into a single RAID 0 array. Would this would give a performance increase? I'd guess no, that it wouldn't make any difference, but I wanted to check before completely ruling it out as a possibility. Or is IBM saying that RAID 00 offers a performance increase only because it allows you to put more than 16 drives in a single logical array?

I'm purchasing a LSI 9260-8i RAID controller for four SSD drives, which supports RAID level 00. We are all about getting the best IO performance in this particular application, so hence the RAID 0.

Banjer
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4 Answers4

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The only way that would improve performance is if by doing so you can gain access to new I/O channels. An example of this would be to use software RAID-0 to stripe across storage attached to two discrete RAID cards on the system, each of which is configured with RAID-0 storage. You would be adding to the number of discrete I/O channels available to service that storage, and would increase its theoretical bandwidth.

In your case you have a 1:1 mapping of ports to drives on a single card. The performance difference between RAID00 and RAID0 would be negligible.

sysadmin1138
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  • That could be done with software RAID0 over multiple controllers as well without having the hardware stripe. – Warner Jul 12 '10 at 16:14
  • @Warner Exactly. The advantage of using a hardware stripe is access to cache optimized for storage, but it isn't required. If you had enough storage that you really did need two separate RAID controllers to cram it all in, RAID00 would allow both controllers to service the same storage requests. On the OP's scale though, it doesn't buy anything. – sysadmin1138 Jul 12 '10 at 16:21
  • I'm not sure I'd accept that as a viable solution for much of anything cache or not. I'd accept benchmarks to prove me wrong, however. ;) – Warner Jul 12 '10 at 16:23
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    @sysadmin1138 - that would be more than 250 drives to require more than one controller (Adaptec 5 series, SAS infrastructure). – TomTom Jul 12 '10 at 16:29
  • @TomTom If your storage access pattern is saturating your controller ports, you may need to add more ports in order to cram in more I/O ops. With RAID0, that level is hit well below the 250 drive limit for SAS. – sysadmin1138 Jul 12 '10 at 17:39
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    @sysadmin1138: look at the cards before you talk ;) There is a 5 series cards with MANY MANY MANY ports. And we talk of a controller tested - IIRC - with 250.000 IOPS. RAID 0 without SSD will not hit that. – TomTom Jul 12 '10 at 18:49
  • @TomTom Which just further proves my point. RAID00 only makes sense if even that (very pretty) 5805Z is not good enough for what you're doing. That's a biiiiiiig I/O system. RAID-double-ought makes sense in a very limited range of I/O access patterns. Most people just need to get a bigger RAID card and get the same performance improvement. – sysadmin1138 Jul 12 '10 at 19:17
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    @sysadmin1138 - get real. Seriously. 250.000 IOPS is, without SSD, something you need about 800 discs with 15000 RPM. In these regions you woulld not be asking about controllers, but about using a HP EVA or another high end SAN. Unless you use SSD it is pretty impossible to get 250.000 IOPS with physical discs. Same - idiocy - on the port limit. A SAS port can handle 1.2 gigabyte of data. You need a LOT of discs to saturate that in a server (random access) pattern. Way more than you can put in physical discs. – TomTom Jul 12 '10 at 21:17
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There would be no performance increase over a RAID0's normal performance with that quantity and type of drives.

Warner
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Do keep in mind that with RAID 0, if you lose a single disk you lose all the data on the volume. If the system has this much IO, I'm guessing that the data is important.

Keith
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mrdenny
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  • Certainly an important thing to note about RAID 0. However, this is just scratch space for SAS jobs (SAS software that is), so the data exists only during program execution. So we are always looking to increase performance, but redundancy is unnecessary. – Banjer Jul 13 '10 at 12:31
  • In that case RAID 0 or 00 would be perfect. IBM does have the XIV platform which I've heard can take massive amounts of IO. They've done some benchmarks on SAS systems and gotten some massive numbers off of them. – mrdenny Jul 13 '10 at 22:21
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I realize this is an ancient question, but it's still valid today.

There is one overriding technical reason to use RAID 00 (or 50, 60, spanned RAID-sets) and that is due to the fact that current RAID sets are limited to 32 physical drives per set. Spanning multiple sets allow you to break that physical boundary while adding performance and, in certain cases, redundancy.

We run special, short-term projects and reconfigure massive arrays of physical disks all the time and are forced to span sets as a result.

Biff Blendon
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