2011-03-30 08:34 AM
We have a dual controller FAS2020 (12x 450GB SAS), currently in active/active mode. We are potentially looking to change to active/passive (as we're only a small environment) to reclaim the space 'wasted' on the 2nd controller due to raid-DP and hotspares, so I was hoping something like this;
6 disks, single aggregate. 2 disks (raid-dp), 1 disk hot spare; 450GB x 6 - 3 = ~1.3TB
6 disks, single aggregate. 2 disks (raid-dp), 1 disk hot spare; 450GB x 6 -3 = ~1.3TB
So a combined usable space of 2.7TB. Now if I were to change to active/passive, i'm guessing I'd have the following;
12 disks, single aggregate. 2 disks (raid-dp), 1 disk hot spare; 450GB x 6 - 3 = ~4TB
0 disks. Simply to be used in the event of controller 1's failure.
Assuming that is correct, is it just of case of making controller 1 take over controller 2's disks, using either the GUI or CLI?
2011-03-30 11:27 AM
This question comes up a lot (the forum really needs a FAQ!).
You can't operate a controller without disks. Both controllers must have a root volume in order to work.
There are a couple of ways to swing this. One is to have a main array with RAID-DP and the secondary one with RAID4. Since the root volume only needs a minimum of 10GB on a FAS2020, you could have a few small volumes on the secondary array.
controller 1 : 9 disks - 6 data, 2 parity, 1 spare = ~2.7TB raw
controller 2 : 3 disks - 1 data, 1 parity, 1 spare = 450GB raw
An alternative way uses RAID4 on both. This has the advantage of better spreading the workload over your two controllers :
controller 1 : 6 disks - 4 data, 1 parity, 1 spare = 1.8TB raw
controller 2 : 6 disks - 4 data, 1 parity, 1 spare = 1.8TB raw (for a total of 3.6TB raw).
These numbers seem small, but remember that deduplication and judicious use of thin provisioning will help you make maximum use of the space.
There is a slight additional risk here in that you'll only tolerate a single disk failure. Since your drives are SAS this is a bit less of a concern than it might be if they were large SATA drives, but the safest route would be to add more disks from an external shelf.
2011-04-05 03:11 AM
OK, didn't realise each controller had to have at least 3 disks. How are Dell (Equallogic), HP (LeftHand) etc doing this then as all their filers are active/passive only without 'loss' of disks on the passive controller?
The problem I have with additional shelves is the shere cost of them. I am fighting with NetApp at the moment how they can charge 50% more for a shelf loaded with 14x 1TB SATA disks (£24k!!!!!!!!) compared to an entire FAS2020 with 12x 450GB SAS disks (£17k). In any other scenario SATA disks are miles cheaper than SAS, so NetApp are somewhere taking the mickey and/or profiteering from their expandability.
On the expandability subject, before we jumped in bed with NetApp, we were told by NetApp that expandability is so much cheaper than the Equallogic (which we were also looking at), as you don't need complete duplicate boxes at the same cost as the main box. Well clearly someone at NetApp needs to go back to school and re-do their Maths exams as 2x Equallogic P4000X boxes totals £34k compared to £17k for a FAS2020 plus £24k for a SATA shelf, which totals £41k.
2011-04-05 04:21 AM
How are Dell (Equallogic), HP (LeftHand) etc doing this then as all their filers are active/passive only without 'loss' of disks on the passive controller?
Actually LeftHand is a prime example of wasting disk space - have a look at this when you have a chance: