Re: RAID growing and --backup-file
On 20/06/15 05:47 AM, PaulNM wrote:
Hey Folks,
I'm attempting to convert a degraded RAID 6 array to a RAID 5
array. Doing that requires either spare devices or a --backup-file
that isn't on the active array.
In this situation, everything is on the array except /boot, which
is on a usb flash drive. Reading up on the backup-file, my
understanding was it's to take care of the critical section which only
consists of a few stripes. Since I didn't think it was used for long,
I felt safe putting it on the flash drive, which is the only available
space anyway.
Well now I have an incredibly slow reshape going on, despite the
normal speed_limit/read-ahead/stripe_cache_size tricks. It's been over
an hour since it started, but the speed is still ~360K/sec and it's
estimated to finish ~94 days from now.
It's pretty clear that it's constantly writing to the backup file,
as there's a bunch of IO still going to it and the system isn't doing
anything else. While the file size has stayed at 57MB, the date keeps
updating and multiple md5sum runs return different hashes.
What are my options at this point? Is there a way to get it to
stop the constant writing to the flash drive, or safely cancel the
operation? Even if waiting months wasn't an issue, the flash drive
will die long before then.
More Details:
Was a 9 x 3TB drive RAID 6 array, one drive failed and was removed.
Wanted to convert to 8 drive RAID 5 array.
mdadm --grow /dev/md0 --level=raid5 --raid-devices=8
--backup-file=/boot/raidbackup2
Wheezy
- PaulNM
I don't think this helps, but a RAID6 array with one failed drive is the
same as RAID5 for all practical purposes. With 8 drives, I'd be very
leery of converting from RAID6 to RAID5. The risk of a second drive
failing while re-adding the first is not negligible.
I think the backup drive allows for the reshape to be interrupted (most
mdadm reshapes can be) but I wouldn't want to bet my data on. Since you
have already done that, backup everything you consider essential then
test whether it can be interrupted. On another machine copy your boot
flash onto a USB external drive and switch it in. If it works, you're set.
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