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Re: [Linux-cluster] Re: GFS on md on shared disks?



Hardware raid is fine, but software raid has it's limitations in this space.

If you can ensure that there will be no failures (in which case, you wouldn't be using raid5), and that the devices are always in the same order, etc -then go ahead.

If you have one machine that has a failure on a drive, only this machine will do the appropriate thing - leaving the others with a view of the device that is inconsistent with that of the machine on which the failure took place. This is the fundamental problem.

 brassow
On Oct 7, 2004, at 11:07 AM, Ed L Cashin wrote:

Erling Nygaard <nygaard redhat com> writes:

No, this will not work at all.

All GFS locking is done on a filesystem level. In order to make this work
you need locking on the blocksystem level .

I guess I'm looking for a concrete reason why it won't work. I've been assuming it won't work, but I can't think of a concrete reason.

You need to lock a resource group to allocate blocks for a file, and
you need to lock the file in order to modify its blocks, so it's not
entirely clear to me why you need block-level locking when md is
involved.

The only concrete problem I can think of is that the md has a
superblock, and no node would know that other nodes are using the same
md superblock.

--
  Ed L Cashin <ecashin coraid com>

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