On September 18, 2006 5:45:08 PM +0200 Jakob Praher <[EMAIL PROTECTED]> wrote:
hi everyone,
I am planning on creating a local SAN via NFS(v4) and several redundant nodes.
huh. How do you create a SAN with NFS?
I have been using DRBD on linux before and now am asking whether some of you
have experience on
on-demand network filesystem mirrors.
I have yet little Solaris sysadmin know how, but i am interesting whether there
is an on-demand
support for sending snapshots. I.e. not via a cron job, but via a kind of
filesystem change
notification system.
AFAIK, Solaris does not export file change notification to userland in
any way that would be useful for on-demand filesystem replication. From
looking at drbd for 5 minutes, it looks like the kind of notification
that windows/linux/macos provides isn't what drbd uses; it does BLOCK
LEVEL replication, and part of the software is a kernel module to export
that data to userspace. It sounds like that distinction doesn't matter
for what you are trying to achieve, and I believe that this block-by-block
duplication isn't a great idea for zfs anyway. It might be neat if zfs
could inform userland of each new txg.
Is this mere a hack or can it be used to create some sort of failover.
E.g. DRBD has the master/slave option, which can be configured easily.
Something like this would
be nice out of the box. So in case of failure another node is the master and if
the former master
is back again, it is simply the slave, so that both have the current data
available again.
Any pointers to solutions in that area are greatly appreaciated.
See if <http://blogs.sun.com/timf/entry/zfs_automatic_snapshots_now_with>
comes close.
I have 2 setups, one using SC 3.2 with a SAN (both systems can access
the same filesystem, yes it's not as redundant as a remote node and
remote filesystem, but it's for HA not DR. I could add another JBOD
to the SAN and configure zfs to mirror between the two enclosures to
get rid of the SPoF of the JBOD backplane/midplane, but it's not
worth it.
The other setup is using my own cron script (zfs send | zfs recv) to
send snapshots to a "remote" (just another server in the same rack)
host. This is for a service that also has very high availability
requirements but where I can't afford shared storage. I do a homegrown
heartbeat and failover thing. I'm looking at replacing the cron script
with the SMF service linked above, but I'm in no rush since the cron job
works quite well.
If zfs is otherwise a good solution for you, you might want to consider
if you really need true on-demand replication. Maybe 5-minute or even
1-minute recency is good enough. I would imagine that you don't actually
get too much better than 30s with drbd anyway, since outside of fsync()
data doesn't actually make it to disk (and then replicated by drbd)
more frequently than that for some generic application.
-frank
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