Re: Quick question regarding RAID1


Jeroen Geilman wrote:
pzaloum@xxxxxxxxx wrote:

I have a raid array currently building using linux software raid
(mdadm) ...

The initial synching of the array naturally takes a good long time to
complete..

Why ? If you have just created this array both members will be empty.
It took roughly 5 minutes on my mirrored 36GB drives.
If you mean you started out with a single drive and later added a mirror to
that, yes, it might take a while, but then I would not do that to begin
with - I'd wipe out both drives, do a quick init and restore from backup.


Yes I am starting from a pre-existing partition on my drive 0 when i
created the array. I did not want the files to be unavailable while
copying them from temporary storage or whatnot into the raid

I was just curious to know: if i do a --remove on one of the array
drive devices and later do a --re-add for the same disk to bring it
back into the array will the resync process take as long as the initial
one? or will it go faster since it virtually has no differences between
itself and the peer drive it is now rejoining?

When you add a drive the system will probably assume it is a replacement -
the copy operation will take just as long in that case.
Unless the raid driver is really smart, and reads the data to compare it
before writing it over.
But that operation is only fast when both drives are guaranteed to be almost
identical in content - if you added a completely new drive this procedure
would take significantly longer than a dumb copy.

Maybe i wasn't clear but the drive i am removing is a previously
healthy mirror. Some minor changes may occur between removal and adding
but generally they will remain identical...


It's a lot more likely that mdadm will just do a dumb copy.

I think the documentation will tell you all you want to know about it.


--
All your bits are belong to us.

.

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