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

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Sean OB_1
Honored Contributor

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


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?
12 REPLIES
Sean OB_1
Honored Contributor

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

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
Outstanding Contributor

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

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
Pete Randall
Outstanding Contributor

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

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

Pete

Pete
Pete Randall
Outstanding Contributor

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

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

Pete
Christopher Caldwell
Honored Contributor

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

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
Honored Contributor

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

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
Honored Contributor

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

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
Honored Contributor

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

Chris made 10+ points indeed!
Pete Randall
Outstanding Contributor

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

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

Pete

Pete
Bill McNAMARA_1
Honored Contributor

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

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
It works for me (tm)
Sean OB_1
Honored Contributor

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

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
Valued Contributor
Solution

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

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