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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.

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3 Answers 3

up vote 8 down vote accepted

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.

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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
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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
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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
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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

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

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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

There would be no performance increase over a RAID0's normal performance with that quantity and type of drives.

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