RE: Use mixed sizes drives in the same Raid string

["Evan Harris" <spanner@xxxxxxxxxx>]

Hi Marco

You can't mix drives of different sizes in 1 RAID set, so the only option is
to configure 2 RAID strings: one with the 70's and one with the 35's. I'd
expect performance issues for this configuration as one RAID set will get
more writes than the other - hopefully someone else can confirm or deny my
thinking on the performance aspect.

Given the amount of work this is likely to create you may want to reconsider
the hardware. It's quite possible that the labour for installing the disks
will greatly exceed the cost of the hardware (that said, I've had many
instances where the labour component wasn't a problem as it was an expense
and the disks were a capital cost; only accountants could be certain that
something that cost more was less expensive).

Keeping in mind that one disk is reserved for parity in each parity set:

Current: 7 X 35 = 245gb available; 213gb occupied = 87%
Proposed: 3 X 70 + 3 X 35 = 315gb available; 213gb occupied = 68%
Possible: 7 X 70 = 490gb available; 213gb occupied = 43%

Around 70 % is still high in my opinion but might be workable for you
depending on what your growth pattern is. If you use 70 gb drives it's
possible you won't need to replace the disks again - certainly for a
considerable period of time.

Regards
Evan Harris


-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Marco Facchinetti
Sent: Wednesday, 14 April 2010 10:55 p.m.
To: midrange-l@xxxxxxxxxxxx
Subject: Use mixed sizes drives in the same Raid string

I'va a customer using 87% of the installed disks (246 Gb) so I have to find
how to increase the total amount of disk space without an expansion unit (no
available slots for new disks).

The machine is  a 9405-520, the controller a 573D-001 with 8 disks (4326),
Raid5 is active. Total available space is  246 Gb.

My 1st question: may I mix in the same raid set drives with diffrent
capacity (eg. 36 and 70 gb)?

If posssible should I expect any perfomance problems?

If not possible should I split the raid in two strings (eg. 4x4326 and
4x4327) or I must change all the drives?

Any suggestion is much appreciated.

TIA

MarcoF