On Sep 25, 2013, at 3:18 PM, Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx> wrote:
> On 9/25/2013 7:56 AM, Stewart Webb wrote:
>> Hi All,
>
> Hi Stewart,
>
>> I am trying to do the following:
>> 3 x Hardware RAID Cards each with a raid 6 volume of 12 disks presented to
>> the OS
>> all raid units have a "stripe size" of 512 KB
>
> Just for future reference so you're using correct terminology, a value
> of 512KB is surely your XFS su value, also called a "strip" in LSI
> terminology, or a "chunk" in Linux software md/RAID terminology. This
> is the amount of data written to each data spindle (excluding parity) in
> the array.
>
> "Stripe size" is a synonym of XFS sw, which is su * #disks. This is the
> amount of data written across the full RAID stripe (excluding parity).
>
>> so given the info on the xfs.org wiki - I sould give each filesystem a
>> sunit of 512 KB and a swidth of 10 (because RAID 6 has 2 parity disks)
>
> Partially correct. If you format each /dev/[device] presented by the
> RAID controller with an XFS filesystem, 3 filesystems total, then your
> values above are correct. EXCEPT you must use the su/sw parameters in
> mkfs.xfs if using BYTE values. See mkfs.xfs(8)
>
>> all well and good
>>
>> But - I would like to use Linear LVM to bring all 3 cards into 1 logical
>> volume -
>> here is where my question crops up:
>> Does this effect how I need to align the filesystem?
>
> In the case of a concatenation, which is what LVM linear is, you should
> use an XFS alignment identical to that for a single array as above.
So keeping the example, 3 arrays x 10 data disks, would this be su=512k and
sw=30?
Chris Murphy
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