Neil Brown wrote:
> On Tuesday October 31, rowe@xxxxxxxxxxxxx wrote:
>> 1 "Warm swap" - replacing drives without taking down the array but maybe
>> having to type in a few commands. Presumably a sata or sata/raid
>> interface issue. (True hot swap is nice but not worth delaying warm-
>> swap.)
>
> I believe that 2.6.18 has SATA hot-swap, so this should be available
> know ... providing you can find out what commands to use.
I forgot 2.6.18 has SATA hot-swap, has anyone tested that?
FWIW, SCSI (or SAS now, using SCSI or SATA drives) has full hot-swap
with completely online drive exchanges. I have done this on recent
kernels in production and it works.
>
>> 2 Adding new disks to arrays. Allows incremental upgrades and to take
>> advantage of the hard disk equivalent of Moore's law.
>
> Works for raid5 and linear. Raid6 one day.
Also works for raid1!
>> 4. Uneven disk sizes, eg adding a 400GB disk to a 2x200GB mirror to
>> create a 400GB mirror. Together with 2 and 3, allows me to continuously
>> expand a disk array.
>
> So you have a RAID1 (md) from sda and sdb, both 200GB, and you now have a
> sdc which is 400GB.
> So
> mdadm /dev/md0 -a /dev/sdc
> mdadm /dev/md0 -f /dev/sda
> mdadm /dev/md0 -r /dev/sda
> # wait for recovery
Could be:
mdadm /dev/md0 -a /dev/sdc
mdadm --grow /dev/md0 --raid-devices=3 # 3-disk mirror
# wait for recovery
# don't forget grub-install /dev/sda (or similar)!
mdadm /dev/md0 -f /dev/sda
mdadm /dev/md0 -r /dev/sda
mdadm --grow /dev/md0 --raid-devices=2 # 2-disk again
# Run a 'smartctl -d ata -t long /dev/sdb' before next line...
> mdadm /dev/md0 -f /dev/sdb
> mdadm /dev/md0 -r /dev/sdb
> mdadm -C /dev/md1 -l linear -n 2 /dev/sda /dev/sdb
> mdadm /dev/md0 -a /dev/md1
> # wait for recovery
> mdadm --grow /dev/md0 --size=max
>
> You do run with a degraded array for a while, but you can do it
> entirely online.
> It might be possible to decrease the time when the array is degraded,
> but it is too late at night to think about that.
All I did was decrease the degradation time, but hey it could help. And
don't forget the long SMART test before running degraded for real. Could
save you some pain.
-Mike
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