Neil Brown wrote:
On Monday June 19, Paul.Davidson@xxxxxxxxxx wrote:
Hi,
I'd like to shrink the size of a RAID5 array - is this
possible? My first attempt shrinking 1.4Tb to 600Gb,
mdadm --grow /dev/md5 --size=629145600
gives
mdadm: Cannot set device size/shape for /dev/md5: No space left on device
Yep.
The '--size' option refers to:
Amount (in Kibibytes) of space to use from each drive in
RAID1/4/5/6. This must be a multiple of the chunk size, and
must leave about 128Kb of space at the end of the drive for the
RAID superblock.
(from the man page).
So you were telling md to use the first 600GB of each device in the
array, and it told you there wasn't that much room.
If your array has N drives, you need to divide the target array size
by N-1 to find the target device size.
So if you have a 5 drive array, then you want
--size=157286400
May I say in all honesty that making people do that math instead of the
computer is a really bad user interface? Good, consider it said. An
means to just set the target size of the resulting raid device would be
a LOT less likely to cause bad user input, and while I'm complaining it
should inderstand suffices 'k', 'm', and 'g'.
Far easier to use for the case where you need, for instance, 10G of
storage for a database, tell mdadm what devices to use and what you need
(and the level of course) and let the computer figure out the details,
rounding up, leaving 128k, and phase of the moon if you decide to use it.
Sorry, I think the current approach is baaad human interface.
--
bill davidsen <davidsen@xxxxxxx>
CTO TMR Associates, Inc
Doing interesting things with small computers since 1979
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