how many disks can be in a raid-5 lun in an FC60?

[Sean OB_1]

I need to know if I can create a lun with 12 disks in it as raid-5 in an FC60 array.

Can this be done?

[Sean OB_1]

Thanks Pete. I'm trying to find out if I can increase a current lun from 6 to 12 disks, or if I'll have to create a second lun let LVM stripe the data across the two luns.

[Pete Randall]

Sean,

I believe you can. The "User's Guide" suggests adding more disk to your RAID 5 LUN "to increase both performance and storage efficiency" without specifying any maximum. There is one example with 6 disks so we can assume that at least that many are permissable.

Pete

[Pete Randall]

Sorry I couldn't come up with anything definitive - still looking, though.

Pete

[Pete Randall]

Sean,

Still not the ultimate answer but I found that the old Model 20 (Nike) arrays could "have 3 to 16 modules bound as a RAID-5 group."

Pete

[Christopher Caldwell]

You should make to LUNs (6 each) instead of 1 LUN (12 each). You lose data resiliency if you go more than 6 deep on a LUN (you'll lose data in certain failures).

[Sean OB_1]

Chris,

Can you give more information on this? In what situation would you lose information with more than 6 disks in the lun?

[Christopher Caldwell]

Fully loaded FC60 is
6 rows with 10 disks each.

This arrangement will handle a single disk failure, a single BCC failure, a single channel failure, or a single controller failure.

If two adjacent disks (in the same row) are in the same LUN, then you lose two disks in a channel failure - thus you lose data integrity with RAID5.

Here's a quote from the admin guide:

"If you attempt to select disks in the same enclosure or on the same channel when binding a LUN, you will be warned that dong so may compromise high availability."

[Eugeny Brychkov]

Chris made 10+ points indeed!

[Pete Randall]

Actually, I think Sean now has a choice to make between high availability and ease of use. It depends entirely on his situation.

Pete

[Bill McNAMARA_1]

if you are going to go more than 6, rather than bottle neck a bus, go to 12... but as mentioned you're no longer HA..

Later,
Bill

[Sean OB_1]

If I go with a 12 disk lun and have the entire lun mirrored to a separate sc30, will the system continue to operate correctly if I lose a channel to one of the sc10's in the fc60?

My assumption is that the system will continue to work off the mirror. Is this correct?

[Quin Hammes · Accepted solution]

Sean,
If this is the client that I think it is, drop me a email at home about this. I helped design the raid configuration and could give you some feedback.


Quin
qhammes@wi.rr.com