On Saturday July 8, reuben-lkml@xxxxxxxx wrote:
> I'm just in the process of upgrading the RAID-1 disks in my server, and have
> started to experiment with the RAID-1 --grow command. The first phase of the
> change went well, I added the new disks to the old arrays and then increased the
> size of the arrays to include both the new and old disks. This meant that I had
> a full and clean transfer of all the data. Then took the old disks out...it all
> worked nicely.
>
> However I've had two problems with the next phase which was the resizing of the
> arrays.
>
> Firstly, after moving the array, the kernel still seems to think that the raid
> array is only as big as the older disks. This is to be expected, however
> looking at the output of this:
>
> [root@tornado /]# mdadm --detail /dev/md0
> /dev/md0:
> Version : 00.90.03
> Creation Time : Sat Nov 5 14:02:50 2005
> Raid Level : raid1
> Array Size : 24410688 (23.28 GiB 25.00 GB)
> Device Size : 24410688 (23.28 GiB 25.00 GB)
>
> We note that the "Device Size" according to the system is still 25.0 GB. Except
> that the device size is REALLY 40Gb, as seen by the output of fdisk -l:
"Device Size" is a slight misnomer. It actually means "the amount of
this device that will be used in the array". Maybe I should make it
"Used Device Size".
>
> Secondly, I understand that I need to use the --grow command to bring the array
> up to the size of the device.
> How do I know what size I should specify?
--size=max
This value can be set with --grow for RAID level 1/4/5/6. If the array was
created with a size smaller than the currently active drives, the extra space
can be accessed using --grow. The size can be given as max which means to
choose the largest size that fits on all current drives.
> How much difference should there be?
> (Hint: maybe this could be documented in the manpage (please), NeilB?)
man 4 md
The common format - known as version 0.90 - has a superblock that is 4K long and is
written into a 64K aligned block that starts at least 64K and less than 128K from the
end of the device (i.e. to get the address of the superblock round the size of the
device down to a multiple of 64K and then subtract 64K). The available size of each
device is the amount of space before the super block, so between 64K and 128K is lost
when a device in incorporated into an MD array. This superblock stores multi-byte
fields in a processor-dependant manner, so arrays cannot easily be moved between com-
puters with different processors.
>
>
> And lastly, I felt brave and decided to plunge ahead, resize to 128 blocks
> smaller than the device size. mdadm --grow /dev/md1 --size=
>
> The kernel then went like this:
>
> md: couldn't update array info. -28
> VFS: busy inodes on changed media.
> md1: invalid bitmap page request: 150 (> 149)
> md1: invalid bitmap page request: 150 (> 149)
> md1: invalid bitmap page request: 150 (> 149)
Oh dear, that's bad.
I guess I didn't think through resizing of an array with an active
bitmap properly... :-(
That won't be fixed in a hurry I'm afraid.
You'll need to remove the bitmap before the grow and re-add it
afterwards, which isn't really ideal.
I'll look at making this more robust when I return from vacation in a
week or so.
NeilBrown
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