On Thu, 2 Nov 2006, Erik Kangas wrote:
I wonder if anyone has played with GFS SAN as an alternateive to NFS that
may/is supposed to have locking-like-local?
http://www.redhat.com/docs/manuals/csgfs/admin-guide/
Or does this have similar deficiencies to NFS?
I don't know.
The requirements of IMAP in general, and UW imapd in particular, ask quite
a lot out of any network filesystem; yet those requirements are quite easy
for a local filesystem to fufill.
The general problem with implementing local filesystem semantics with a
network filesystem is the balancing of performance with filesystem
semantics. It is easy enough to implement a network filesystem in which
all filesystem operations do a client/server interchange and block until
the interchange is completed. However, the performance of such a
filesystem would disappoint most people; RTTs are not your friend in any
network protocol.
Since most applications do not need all the local filesystem semantics,
network filesystems generally cheat in order to get (substantially) better
performance. The most common cheat is to use local caches instead of
a network round-trip.
The problem is when the application really needs those semantics. Not
many applications have multiple sessions doing random updates of the same
data simultaneously; but that's what IMAP does.
-- Mark --
http://staff.washington.edu/mrc
Science does not emerge from voting, party politics, or public debate.
Si vis pacem, para bellum.
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