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My understanding of RAID 0 is that the data is split and striped across all of the drives in the array. If there is only one drive in the array, then what is the point of a single drive RAID 0 array and how does it work?

From these ceph benchmarks it appears there is a tangible performance difference as compared to JBOD in at least some cases.

Despite my best Googling I could not find anything substantial. Thanks!

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The difference is whatever the particular implementation wants it to be. It can be everything or nothing. There's really no such thing as "single drive RAID 0", so a particular RAID implementation can mean anything by it. –  David Schwartz Jan 23 '13 at 5:05

5 Answers 5

up vote 8 down vote accepted

In the case of this implementation (the LSI SAS2208 controller), JBOD does not use on-board cache, single disk RAID0 uses on-board write-back cache. The ceph benchmark explains it in the test setup. The performance increase comes from caching not striping. Most RAID controllers allow you to setup single disk RAID0 or RAID1 as a way to support JBOD, this controller is a little different in that it also supports JBOD (without any controller cache).

There are cases where RAID levels can use less disks than you normally think, and still provide increased performance or redundancy. For example Linux md RAID10 can be used with two or more disks, including odd numbers of disks, unlike traditional RAID10 which would require four or more disks and even numbers. Linux md RAID10 with two disks is faster than RAID1.

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Wow, thanks for the great answer! –  JKnight Jan 25 '13 at 5:12

Just my thoughts...once upon a time I had an old PC with no SATA ports. Me knowing nothing bought a raid adapter card and set up a single HDD in Raid with the SATA Hard Drive. Not sure of the raid mode but I'm guessing it was Raid0...And guess what...It works. Today I find myself looking to do the same thing. I have a new Asus Mother board which has NO raid and NO Ahci. I got an awesome SSD that runs at about 20% of its actual speed due to it having to run on the IDE controller. So I'm going to buy the Raid Adaptor card and run my SSD in Raid0 just so I can make use of the faster controller.

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Drives plugged into a RAID controller are not necessarily in any RAID configuration whatsoever, but just like a video card you can find something much better than what came on the motherboard. –  chicks Jun 21 at 5:20
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This isn't really an answer, hence your downvotes - on ServerFault this is better left as a comment. –  Paul Dixon Jun 21 at 7:24

RAID-0 on single disk is used mostly on SSD disks, which acts as Cache disk (Intel Smart Response). When you activate "accelerate mode" for any HDD or RAID Volume via SSD Cache, IRST driver converts disk to RAID-0 Volume. If you are not using whole disk space, there will be automatically created second RAID-0 Volume, which can be used for other data. My example:

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I am not sure, why it has to be in RAID mode, as I see no benefit from it. Maybe for some specific operations there is minor boost.

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It's also useful to mention here that some server configurations require you to load the RAID regardless of how many physical disks are actually present.

For example, a server chasis where you can only access the disks through a controller board.

In this scenario, RAID 0 is the default setup.

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For me JBOD is the default. With RAID0 I might have to work harder to bring up the drive on another system. –  chicks Jun 21 at 13:42

There is no such thing as a single drive RAID 0 array. In order to setup a RAID 0 array, you would need two or more disks. I think you are mis-reading the test setup in the article you reference.

However, you are correct, in that in a RAID 0 array (note not RAID 0 mode) data is striped across all disks in the array. This is an odd RAID level as there is no real redundancy, as a failure of one drive will fail your array. RAID 0 will give you the total amount of space available on all disks for your array as long as they are the same size, with no redundancy or fault tolerance. If they differ in size, each disk will be relegated to the size of the smallest disk in the array.

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