"Universal" Online Spare Drive

[Jim Mulgrew]

Is it possible to assign a single drive within a server (or storageworks) as the online spare for more than one array? Did that just make sense? (grin)

Let's say we have a storageworks array attached to our server. Within that storageworks there are 2 RAID5 arrays set up. Instead of assigning a drive to each array as an online spare, is it possible to use just one for this need?

- Jim

[Leif Halvarsson_2]

Hi,
I suppose you mean two RAID 5 sets in one array. As you don't mention which disk array you talk about my answere is general. Most (all ?) modern arrays that uses conventional RAID tecnology (dedicated RAID sets) support global hot spare disk. If you mean VA or EVA arrays it is a little different as those array don't use dedicated spare disks but use a "spare area" on each disk. If one disk fails the data on that disk can be recovered using the "spare area".

[Uwe Zessin]

Jim,

you question makes sense, yes. You don't say what array you are asking about...

The HSG60/80 controllers have only 'global' spare disks. If the size fits or is greater than the failed disk, any potential spare disk can be used - there is a replacement policy an each RAID-1 or RAID-5 storage set than can decide for best-size-fit or best-performance-fit (choose a disk based on controller SCSI bus).

The VA7000 series and EVA-3000 /-5000 storage array don't have 'spare disks' at all. They include the physical disks in their disk groups and distribute their capacity equally over all disks. The advantage is that the I/O capacity of the 'spare disks' can be used for real work, too. Otherwise a spare disk is just spinning, but its read/write heads are not doing any useful work. The (small) downside is that the disks are just members of the disk group (VA: redundancy group). You need additional spare capacity in other groups. Virtual disks are then carved from the disk group and presented to the servers. Their data is distributed equally over all disks - that is called (load) leveling.

The MSA1000 storage array has dedicated spare disks. It allows the user to assemble disks together to an 'array' and then carve any logical disks from it, but it is nowhere as flexible as VA and EVA - you can only delete logical disks from an array in reverse order.

You assign a spare disk to an array, but I can't tell you at the moment if it is possible to assign a spare disk to multiple arrays.

Well, that got a little long, but I hope it makes sense to you ;-)

[Jim Mulgrew]

Sorry all, I did leave that out. I'm referring to 4200 and 5300 series controllers with arrays on them. Sorry about that.

[Uwe Zessin]

Ah, the backplane Smart Array controllers...
Don't know about the 4200, but the 5300 does support multiple spare disks per array and sharing of a spare disk by multiple arrays.