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I'm trying to create two RAID10 arrays using LSI MegaRAID's WebBIOS utility.

If I understand correctly, I must create many two-disk RAID1 pairs called "disk groups" and then span those disk groups together to get the striping layer. Then I can afford to lose one drive from every two-drive RAID1 disk group without suffering a data loss. Right?

The problem is that I have 10 SSD drives and 10 SAS drives. But I can only create 8 disk groups. That's 16 drives. What gives? Will I have to settle for RAID01 creating 5-drive RAID0 and mirroring it with another such array?

Controller: Supermicro AOC-USAS2LP-H8iR (LSI 2108 chip)

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migrated from serverfault.com Apr 26 '11 at 14:11

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For a RAID-10 of 20 drives (for example): 2 'groups' of 10 drives (2 RAID-1 'mirrors', 5 drives per side in each mirror), striped (RAID-0).

See here for some info that may help clarify your options.

Perhaps 2 RAID-10's made from 9-drive, 3-way RAID-1's, with a hot spare (the 10th drive) for each RAID-10? :)

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I know what RAID10 is. The problem is that the WebBIOS utility is preventing me from adding more than 8 drive groups. I created 5 drive groups (of 2 drives each) and then I created RAID0 span over those 5 drivegroups. All was fine. But I could not repeat that process to create a second RAID10 array: the utility hid the button to create a new data group after there was already 8 datagroups. –  Henno Apr 26 '11 at 14:50
    
The main point is, a mirror/group can contain more than 2 drives, and must, to do what you want to do. Regardless, usually in the MegaRAID BIOS you select all the drives you want to use in an array (ie: select 10 drives you want in a RAID10) and then it should give you the option to make a RAID10 from those drives; no need to make the mirrors first. –  Ƭᴇcʜιᴇ007 Apr 26 '11 at 14:55
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We revisited WebBIOS once more and this time we were able to create five disk groups, add them to a span and make that RAID10. Then we selected configuartion wizard, add, manual and redid. This time we could create more than 8 disk groups. Perhaps we missed something obvious last time. –  Henno Apr 26 '11 at 15:49

Late answer to this but I've recently been benchmarking a new 32 disk array and I've got two observations:

  1. If one creates a single RAID-1 drive group of 16 pairs (32 total), then striping occurs within the drive group. The RAID-1 specification says "no striping" but in a drive array, my tests show striping is going on - data is definitely spread across all disks in the RAID-1 drive group. Which makes sense otherwise the OS would favour the 1st drive pair first and not use the last drive pair until the VD was nearly full - not good for overall drive usage
  2. LSI Logic documentation says to create RAID-10, you create two drive groups and then span them together. You can create up eight spans. One infers that if this is setting up striping, the more spans the better. Benchmarking shows the opposite. A single RAID-1 drive group of 16 pairs performs better on all CrystalDiskMark tests than 8 spans of 2 pairs

So based upon benchmarks alone (with caveats), you get better performance with a single so-called RAID-1 span of 16 pairs than what LSI called RAID-10. Which feels more like RAID-100 IMO.

Make of this what you will!

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Related topic you may find interesting: serverfault.com/questions/517729/… –  Henno Jul 9 '13 at 9:24

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