Re: Removing devices from RAID-5

[Justin Piszcz <jpiszcz@lucidpixels.com>]

> > > I would think that
> > > mdadm --grow --raid-devices=4 -z max /dev/md1 /dev/hdg2 /dev/hde2
> > > /dev/sda2 /dev/hdk2

Make sure the new device is added as a spare first the -z should not be 
needed, by default it should use all space on the new drive.

On Thu, 14 Jun 2007, Justin Piszcz wrote:

>
>
> On Thu, 14 Jun 2007, Rich Walker wrote:
>
>> Justin Piszcz <jpiszcz@lucidpixels.com> writes:
>> 
>>> On Thu, 14 Jun 2007, Rich Walker wrote:
>> 
>> [snip]
>>>> 
>>>> The array is used as a single PV/VG for LVM.
>>>> 
>>>> What I want to do is to
>>>> (a) reduce the PV/VG so it would fit in 160*3 rather than 160*4
>>>> (b) remove the last 160GB drive, (hdi), taking the array from 4+1 to 4+0
>>>> (c) rearrange the array from 4+0 to 3+1
>>>> (d) grow the array to 250*3
>>>> (e) enlarge the PV/VG again.
>>>> 
>>>> I would think that
>>>> mdadm --grow --raid-devices=4 -z max /dev/md1 /dev/hdg2 /dev/hde2 
>>>> /dev/sda2 /dev/hdk2
>>>> would do steps (b),(c),(d) in one go - is this correct?
>>>> 
>>>> The linux kernel version running is 2.6.21.3 SMP.
>>> 
>>> As far as I know you cannot shrink any md raid in Linux.
>>> 
>>> Justin.
>> 
>> Step (c) shrinks the array, which would be a problem.
>> 
>> But the mdadm command given *should* actually grow the array (from 640GB
>> to 750GB) whilst reducing the number of disks...
>> 
>> Is this likely to work?
>> 
>> mdadm says:
>> 
>> thoth:/--# mdadm --grow --help
>> Usage: mdadm --grow device options
>> 
>> This usage causes mdadm to attempt to reconfigure a running array.
>> This is only possibly if the kernel being used supports a particular
>> reconfiguration.  This version only supports changing the number of
>> devices in a RAID1, and changing the active size of all devices in
>> a RAID1/4/5/6.
>> 
>> Options that are valid with the grow (-G --grow) mode are:
>>  --size=        -z   : Change the active size of devices in an array.
>>                      : This is useful if all devices have been replaced
>>                      : with larger devices.
>>  --raid-disks=  -n   : Change the number of active devices in a RAID1
>>                      : array.
>> thoth:/--# mdadm -V
>> mdadm - v2.5.6 - 9 November 2006
>> thoth:/--#
>> 
>> which makes me think it wouldn't...
>> 
>> cheers, Rich.
>> 
>> -- 
>> rich walker         |  Shadow Robot Company | rw@shadow.org.uk
>> technical director     251 Liverpool Road   |
>> need a Hand?           London  N1 1LX       | +UK 20 7700 2487
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>> 
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>
> You can try it, otherwise grab the latest version of mdadm and go ahead and 
> grow it.  I have grown a 1.8TB array to 3.3TB and it was a pretty old version 
> of mdadm.
>
> Justin.
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