On Wed, Jan 24, 2007 at 12:58:03PM +0100, Alan Marco IsiMan wrote: > We're going to install a new email platform and we have a big doubt. > What is better for our /var/mail, OCFSv2 or NFS? I mean, SAN or NAS. > There'll be three machines reading /var/mail and writing in it (webmail > write in sent folder and courier-imap in all folders). Courier-Imap is > good for NFS? Has someone installed OCFSv2 for /var/mail?
I can give you feedback on the NFS solution. This works very well - I built a very large cluster based around this (with hundreds of thousands of accounts, mostly POP3 users). This has two exim boxes receiving incoming mail, four courier POP3+IMAP boxes, two sqwebmail boxes. The NFS server is a clustered pair of Network Appliance devices (www.netapp.com). This really is the crucial part: the NetApp's WAFL filesystem gives extremely high performance under the heavy create-write-read-delete load which such a mail system generates. Don't be tempted to build your own NFS server with (horrors) a RAID5 array; its performance will be dreadful. Mirrored pairs of disks will be better, but still nowhere near what the Netapp achieves (although maybe sufficient for your purposes, given that the NetApp is very expensive). BTW I would avoid ReiserFS: I have had very bad experience with data loss. Essentially there are no fsck-like tools for data recovery with ReiserFS - a limitation that the author freely admits. Once it's corrupted, everything is lost. Building an NFS server using OpenSolaris and ZFS looks like a promising solution, as ZFS implements many of the good ideas from WAFL, but I've not tried it and it's unclear how ready it is for prime-time. As for OCFS: I have no experience. I see that v2 is supposed to have POSIX filesystem semantics, which v1 didn't; Maildir relies heavily on POSIX semantics, in particular atomic moves of files between directories. You could build a hybrid solution: that is, you can build an OCFS2 storage server, and then export its contents via NFS to the mail front ends. See http://oss.oracle.com/projects/ocfs2/dist/documentation/ocfs2_faq.html#NFS Using this approach would make it easy to scale horizontally by adding more NFS servers, and/or to migrate to a different NFS server later should you wish to do so. If you don't want to use NFS or a global filesystem, then your other option is to build a proxy-based cluster. This means you build a series of small independent mail servers, each with local disk and holding a subset of your users accounts. The incoming POP3/IMAP connections are each redirected to the right cluster member. Unfortunately, sqwebmail does not currently implement such proxying. Which way you go is going to depend to a large degree on your user load: e.g. whether you are building an enterprise mailserver for 100 users, or an ISP mailserver for 100,000 users. If you are going to make use of IMAP then you should do some very careful testing before going live. I have heard cases of people reporting systems maxing out their disk subsystems with only a few tens of IMAP users logged in. Unfortunately these cases don't ever seem to have been properly investigated, to find out whether the cause is something to do with the filesystem, the IMAP server, the client behaviour, or some combination of these. You may end up having to do this investigation yourself. However, it does seem that special care is needed with FAM/GAMIN, the daemon which notifies the IMAP server of filesystem changes. Some people on this list have said that FAM causes their system to fail, but replacing the FAM packakes with GAMIN fixes everything. Personally I built courier-imap without FAM support entirely. Unfortunately there is no ./configure option to do this; you just have to remove fam and fam-devel from your system before building. Regards, Brian. ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Courier-imap mailing list [email protected] Unsubscribe: https://lists.sourceforge.net/lists/listinfo/courier-imap
