Re: -z not on RAID0 / MPIO hurdle

[Goswin von Brederlow <goswin-v-b@web.de>]

mark delfman <markdelfman@googlemail.com> writes:

> Hi Goswin,
>
> I am not sure that this would work well for us... we would have you
> use LVM to create individual block targerts, then use MD to create
> RAIDs and then LVM again to create pools.

Last I tried raid on lvm would mess with the idle I/O
determination. The raid rebuild would cause I/O on the device mapper
and then raid things the user is doing I/O and slows the raid rebuild
down to the minimum speed.

> We would ideally stay to LVM on all our raids (whether 0 / 6 etc). so
> would like to keep it in there...
>
> Does any know if there is a reason -z doesn’t work with RAID0 (i mean
> is it designed to not work because of abc reason, or simply its never
> been needed etc)?
>
>
> Thank you for you help
>
>
> Mark D
> On Thu, Aug 13, 2009 at 3:06 AM, Goswin von Brederlow<goswin-v-b@web.de> wrote:
>> mark delfman <markdelfman@googlemail.com> writes:
>>
>>> Hi.... I am hopeful that the group could provide me with some advice
>>> regarding limiting the drive size on a RAID0.  I know and use the –z
>>> option for other raid levels, but this seems to have no effect on
>>> RAID0.
>>>
>>> I am sure many will ask ‘why bother’ or ‘use fdisk’ but the problem is:
>>>
>>> We need to have some preserved information on each drive – can be only
>>> a few MB at the end of the drive for example
>>> In the past we have simply used Fdisk to partition, save our data on
>>> Sdx2 and used Mdadm on Sdx1  (which works fine)
>>> But we are looking to move to dual channel SAS drives and use DM MPIO
>>>
>>> DM MPIO works fine also, but not on the partitions, only the whole
>>> drive.  So when we MDadm DMx it overwrites the SdX2 partition etc.
>>>
>>> The answer was that we used the –z and limited the drive size and
>>> simply used DD to write our data to the end LBA’s....
>>>
>>> But on RAID0 the –z does not seem to function, so I cant think of a
>>> way around this   (other than changing the LBA range in the drive and
>>> this is restricted I think)
>>>
>>>
>>> Does anyone have any ideas?  I appreciate any help
>>
>> LVM and --setphysicalvolumesize on pvcreate?
>>
>> MfG
>>        Goswin
>>

MfG
        Goswin
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