On 1 Feb 2010, at 11:58, J. Roeleveld wrote:
...
I am currently installing a new server and am using Linux software
raid to
merge 6 * 1.5TB drives in a RAID5 configuration.
Creating the RAID5 takes over 20 hours (according to " cat /proc/
mdstat ")
Is there a way that will speed this up? The drives are new, but
contain random
data left over from some speed and reliability tests I did. I don't
care about
keeping the current 'data', as long as when the array is reliable
later.
Can I use the " --assume-clean " option with mdadm and then expect
it to keep
working, even through reboots?
Or is this a really bad idea?
It wasn't my intention to chide you - I don't use software RAID
myself, and your question piqued my curiosity - but the first three
Google hits for "assume-clean" indicate that this isn't safe to use
with RAID5.
The 4th Google hit contains an extract from the manpage:
... It can
also be used when creating a RAID1 or RAID10 if you want
to avoid the initial resync, however this practice --
while normally safe -- is not recommended. Use this
only if you really know what you are doing.
I have to say that I don't fully understand this. I would have thought
that one could pretend the entire array was empty, and the RAID driver
would just overwrite the disk as you write to the filesystem. The
parts used by the filesystem are the only parts you care about, and I
wouldn't have thought it would matter if the unused parts weren't in
sync. I would be delighted if someone could explain me.
I kinda expected this 20 hours to be spent verifying that the disks
contain no bad sectors, which would really hose you if it were the case.
But OTOH, 20 hours does not seem an outrageous amount of time for
building a 7.5TB array. You're not going to do this often, and you
want it done right.
It would be interesting to know whether hardware RAID would behave any
differently or allow the sync to perform in the background. I have
only 1.5TB in RAID5 across 4 x 500gb drives at present; IIRC the
expansion from 3 x drives took some hours, but I can't recall the
initial setup.
Stroller.
