On Jan 14, 2007, at 21:37, Wee Yeh Tan wrote:
On 1/15/07, Torrey McMahon <[EMAIL PROTECTED]> wrote:
Mike Papper wrote:
>
> The alternative I am considering is to have a single filesystem
> available to many clients using a SAN (iSCSI in this case). However
> only one client would mount the ZFS filesystem as read/write
while the
> others would mount it read-only. For my application, all files are
> written once then only ever read or deleted.
I know this doesn't work for UFS. I'm fairly certain this won't
work for
ZFS for many of the same reasons. (Writes in any hosts buffer cache,
inflight transactions, metadata updates, etc.) Why not use NFS?
The reason why it wouldn't work is because of the system caching
reads. The FS assumes that it knows everything that is going into/out
of the file system but this is not true in a parallel file system.
What you will find is that while you can mount the UFS (ZFS should
prevent mounting but that's another story), any updates on previously
read files will not be visible.
I agree that you should look at NFS.
Or just use QFS - this will do exactly what you want, plus you'll
also have
the option to go multi-writer if you so wish. As for the issue of
local buffer
cache synchronization you can set the invalidation rate, or just
completely
defeat the buffer cache if you wish with per file and per directory
semantics
that can be set on the fly. DIRECTIO might suck for certain types of
random
IO that may not align on a backend storage stripe, but it sure does help
with multi-node synchronization .. (cache on the storage end and build
your volumes there instead) .. i think you'll find it works
wonderfully with
iSCSI and if you want to integrate with ZFS - i'd think about using
zvols
aligned with the QFS DAU and directio (so you don't double buffer
between
QFS and the ZFS COW which will always buffer)
In my mind QFS would have been a much better base for integration of the
ZFS feature set -- the flexibility, performance, and scalability are
wonderful
.. but alas - project funding, politics, and pride can be a cruel
mistress
particularly when you have differences of opinion in FS design
philosophy
(older Cray programmers vs newer VM programmers)
oh .. in case you've never heard of QFS for whatever marketing reason:
http://www.sun.com/storagetek/management_software/data_management/qfs/
give it a try .. free download with no lockdown key ..
.je
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