Re: Removing devices from RAID-5

[Rich Walker <rw@shadowrobot.com>]

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.

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