[lustre-discuss] backup zfs MDT or migrate from ZFS back to ldiskfs

[Raj]

Stu,
Is there a reason why you picked Raidz 3 rather than 4 way mirror across 4
disks?
Raidz 3 parity calculation might take more cpu resources rather than
mirroring across disks but also the latency may be higher in mirroring to
sync across all the disks. Wondering if you did some testing before
deciding it.

On Fri, Jul 21, 2017 at 12:27 AM Stu Midgley <sdm900 at gmail.com> wrote:

> we have been happily using 2.9.52+0.7.0-rc3 for a while now.
>
> The MDT is a raidz3 across 4 disks.
>
> On Fri, Jul 21, 2017 at 1:19 PM, Isaac Huang <he.huang at intel.com> wrote:
>
>> On Fri, Jul 21, 2017 at 12:54:15PM +0800, Stu Midgley wrote:
>> > Afternoon
>> >
>> > I have an MDS running on spinning media and wish to migrate it to SSD's.
>> >
>> >     Lustre 2.9.52
>> >     ZFS 0.7.0-rc3
>>
>> This may not be a stable combination - I don't think Lustre officially
>> supports 0.7.0-rc yet. Plus, there's a recent Lustre osd-zfs bug and
>> its fix hasn't been back ported to 2.9 yet (to the best of my knowledge):
>> https://jira.hpdd.intel.com/browse/LU-9305
>>
>> > How do I do it?
>>
>> Depends on how you've configured the MDT pool. If the disks are
>> mirrored or just plan disks without any redundancy (i.e. not RAIDz),
>> you can simply attach the SSDs to the hard drives to form or extend
>> mirrors and then detach the hard drives - see zpool attach/detach.
>>
>> -Isaac
>>
>
>
>
> --
> Dr Stuart Midgley
> sdm900 at gmail.com
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>
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