-z not on RAID0 / MPIO hurdle

-z not on RAID0 / MPIO hurdle

[mark delfman]

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
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Re: -z not on RAID0 / MPIO hurdle

[Goswin von Brederlow]

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
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Re: -z not on RAID0 / MPIO hurdle

[mark delfman]

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.

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
>
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Re: -z not on RAID0 / MPIO hurdle

[Goswin von Brederlow]

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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Re: -z not on RAID0 / MPIO hurdle

[Luca Berra]

On Wed, Aug 12, 2009 at 07:44:10PM +0100, mark delfman wrote:
>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.
run kpartx on the dm device, it should create mappings for the single
partitions.
L.

-- 
Luca Berra -- bluca@comedia.it
         Communication Media & Services S.r.l.
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Re: -z not on RAID0 / MPIO hurdle

[mark delfman]

Thank you Luca!  much appreciated

On Fri, Aug 14, 2009 at 4:35 PM, Luca Berra<bluca@comedia.it> wrote:
> On Wed, Aug 12, 2009 at 07:44:10PM +0100, mark delfman wrote:
>>
>> 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.
>
> run kpartx on the dm device, it should create mappings for the single
> partitions.
> L.
>
> --
> Luca Berra -- bluca@comedia.it
>        Communication Media & Services S.r.l.
>  /"\
>  \ /     ASCII RIBBON CAMPAIGN
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