[CentOS] extend raid volume - new drive

James Bensley jwbensley at gmail.com
Tue Apr 28 10:48:42 UTC 2009


Hi there,

Just to clarify; You have two 1TB disk that are mirrored (raid 1)?

Normally a mirror can't be extended as the mirror is between block 0
to 1000000 (for example if 1000000 was the end of the drive) on one
drive with block 0 to 1000000 on the other (if you have used block
level mirror, you could of chosen byte level mirroring?). With RAID 1,
mirrors require an even number of disks.

You haven't said how large you knew drive (sdc) is? Is it 500GBs or
1000? If for example it was 1000, you would need to buy another 1000GB
drive, and set up a second mirror with the two new drives. So now you
have two 1TB mirrors and stripe across them
(http://en.wikipedia.org/wiki/Nested_RAID_levels#RAID_10_.28RAID_1.2B0.29)
giving you 2TB of space that is mirrored also for redundancy (then you
would have the redundancy of mirroring plus the speed of striping, or
near there).

You could go the route of turning it into a Raid 5 as mentioned by "D"
which would give you a middle man in that its a bit faster than a
mirror (but not as fast as a stripe) and you still have some
redundancy against a drive failure (but not as much as a RAID 1+0).

How is you RAID set up, is it software or hardware? If hardware, what
raid controller/card are you using? How much are you looking to extend
the storage capacity by? How much does redundancy matter to you? Do
you just want speed (i.e. a stripe, RAID 0)?

A few more details would be great.

James ;)

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