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Re: [Linux-cluster] Distributed Replicated GFS shared storage



José Miguel Parrella Romero wrote:
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Juliano Rodrigues escribió, en fecha 30/09/08 10:58:
Hello,

In order to design an HA project I need a solution to replicate one GFS
shared storage to another "hot" (standby) GFS "mirror", in case of my
primary shared storage permanently fail.

Inside RHEL Advanced Platform there is any supported way to accomplish
that?

I believe the whole point of GFS is avoiding you to spend twice your
storage capacity just for the sake of storage distribution. It already
enables you to have a standby server which can go live through a
resource manager whenever you need it.

Look like the original subject (requirement) is to have redundant (HA) storage devices. GFS alone can't accomplish this since it only deals with server nodes - as soon as the shared storage unit is gone, the filesystem will be completely unusable.

Depending on the hardware, redundant storages do not necessarily consume a great deal of storage capacity. Though GFS itself does spread the blocks allocation across the whole partition (to avoid write contention between multiple clustered nodes), the underneath hardware may do things differently. That is, GFS block numbers (and its block layout) do not necessarily resemble the real disk block numbers (and the physical layout). So, say if you have a 1TB GFS partition configured but it only gets half full, you may have extra 500GB space to spare if your SAN product allows this type of over-commit. If your storage vendor supports data de-duplication, the storage consumption can go down even further.
-- Wendy

However, if you need to have two separate storage facilities which sync
in one way, DRBD is probably the easiest way to do so. Heartbeat can
manage DRBD resources at block- and filesystem-level easily, and other
resource managers can probably do so (though I haven't used them)

HTH,
Jose
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