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Hi list,

I'm looking for advices / experiences concerning PostgreSQL with data
storage on NAS via NFS. I've found a few references in the archives or
the docs, but they are old, and opinions differ:
. "There are a lot of horror stories concerning running databases (not
only Postgres) over NFS."
http://archives.postgresql.org/pgsql...6/msg00217.php
. "NFS and other remote file systems are not recommended for use by
POSTGRESQL. NFS does not have the same file system semantics as a local
file system, and these inconsistencies can cause data reliability or
crash recovery problems."
http://www.postgresql.org/files/docu...ce/node11.html
. "The problem with NFS is not so much the protocol, but whether your
server is reliable. If you trust that your NAS device is reliable
enough, then you should be OK."
http://archives.postgresql.org/pgsql...1/msg01362.php

The NAS would be from LaCie, using 4 disks (Raid5 + spare)
(http://www.lacie.com/fr/products/product.htm?pid=10876), mounted via
NFS from a Linux server running Postgresql .

What are the implications with regard to PostgreSQL performance and
(more important) reliability?


Thanks in advance.
Regards,
--
Jean-Denis Girard

SysNux Systèmes Linux en Polynésie française
http://www.sysnux.pf/ Tél: +689 483 527 / GSM: +689 797 527

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TIP 2: Don't 'kill -9' the postmaster

I've had trouble with NFS files on nfs filesystems disappearing for a
second and reappearing. I had to add a retry loop with a delay in my
code that does file reading. I wouldn't try running a production level
postgres over nfs.

On 28.07.2007 06:48, Jean-Denis Girard wrote:
> The NAS would be from LaCie, using 4 disks (Raid5 + spare)
> (http://www.lacie.com/fr/products/product.htm?pid=10876), mounted via
> NFS from a Linux server running Postgresql .

Sorry, but that sounds like a sick setup..

1.) RAID 5 is a bad choice for a DBMS, due to implicit reads caused by
parity calculation.
2.) Most cheap NAS (such as this one) have way to high latency for a DBMS.
3.) NFS is nothing you want to have a DBMS running on top.
4.) I don't think this device has battery backed cache.
5.) At least I have bad experiences with Lacie storage devices (Bigger
Disk Extreme)


To sum it up.. I'd say what you get with that setup is a dead slow,
unstable PostgreSQL experience with a good chance of data corruption on
power failure.


--
Regards,
Hannes Dorbath