Adding HDD to an existin RAID 5 device?

Adding HDD to an existin RAID 5 device?

Post by bozothedea » Sat, 22 Nov 2008 18:14:03

Hi, all.

I have a StorEdge3320 with 5 HDD in a RAID5 config. I want to add a
few more HDD to this config. Is it possible to add HDD to an existing
RAID5, or does the existing RAID5 need to be taken down and a new
RAID5 created with all the HDD?


Adding HDD to an existin RAID 5 device?

Post by Michael La » Sun, 23 Nov 2008 04:21:46


Probably depend on what RAID that is, atleast on ZFS you can not do
that, you can add 5 more in a second config(vdev) and add that to the
current pool thereby easy increasing
the pools size.

If adding 5 more would be away to go then ZFS could be something to
think about if you can can use Solaris 10.



Adding HDD to an existin RAID 5 device?

Post by DoN. Nicho » Sun, 23 Nov 2008 12:33:00

I think that depends on the implementation of RAID-5. I don't
know the StorEdge3320, but I do know that with Sun's zfs, you can do a
lot of things to a running array, among which are to add more drives
(though removing drives (other than hot spares) is not possible, unless
it has been added to the latest Solaris 10 (u6) download, which I have
not yet installed and played with. I discovered the inability to remove
by accidentally making a hot spare into an additional disk in an array.
To fix that, I had to create a new array and copy everything over.

One thing that I have done is taken a running array of five 18
GB SCA drives (in raidz2 -- the double-parity version of RAID-5 in zfs)
and two hot spares, and migrated to the same number of 33 GB FC drives,
by issuing the command:

replace [-f] <pool> <device> [new_device]

as in:

replace -f home-p c4t2d0 c2t10d0

then waiting for the resilver to be complete, then repeating the command
for the next disk in the array, and so on. The size of the pool
remained constant until the last drive (the second hot spare) was
replace, after which the size of the pool jumped to the appropriate
value for the larger drives. All this time, the filesystems on that
pool were in constant use.

Later, I did the same thing again, but replacing the 33 GB FC
drives with 76 GB FC drives, bouncing off another (non-hot) spare.

So -- the system is very flexible, even back in the version
which comes with an earlier version of Solaris 10 (Generic_118833-33).

Others will have to tell you what you can do with the setup
which you have. I would expect the ability to grow the array to be
present, but I'm not sure.

Note that zfs suggests a maximum number of drives in a given
pool, and suggests that you use more drives by forming two or more pools
with the maximum number of drives or fewer, and then merging the
resulting pools into a larger filesystem. Apparently, the efficiency
falls when you get too many drives in a given pool.

Good Luck,

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