On Wed, Aug 15, 2012 at 4:50 AM, John Robinson
<john.robinson@xxxxxxxxxxxxxxxx> wrote:
> On 15/08/2012 01:49, Andy Lutomirski wrote:
>>
>> If I do:
>> # dd if=/dev/zero of=/dev/md0p1 bs=8M
>
> [...]
>
>> It looks like md isn't recognizing that I'm writing whole stripes when
>> I'm in O_DIRECT mode.
>
>
> I see your md device is partitioned. Is the partition itself stripe-aligned?
Crud.
md0 : active raid6 sdg1[5] sdf1[4] sde1[3] sdd1[2] sdc1[1] sdb1[0]
11720536064 blocks super 1.2 level 6, 512k chunk, algorithm 2
[6/6] [UUUUUU]
IIUC this means that I/O should be aligned on 2MB boundaries (512k
chunk * 4 non-parity disks). gdisk put my partition on a 2048 sector
(i.e. 1MB) boundary.
Sadly, /sys/block/md0/md0p1/alignment_offset reports 0 (instead of 1MB).
Fixing this has no effect, though.
--Andy
--
Andy Lutomirski
AMA Capital Management, LLC
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