2006/11/17, Sarah Walters <s.walters@xxxxxxxxxxxxx>:
> -----Original Message----- > From: info-cyrus-bounces@xxxxxxxxxxxxxxxxxxxx > [mailto:info-cyrus-bounces@xxxxxxxxxxxxxxxxxxxx] On Behalf Of > Igor Zhbanov > Sent: Friday, 17 November 2006 10:32 AM > To: info-cyrus@xxxxxxxxxxxxxxxxxxxx > Subject: Re: Cyrus IMAP and MySQL mailboxes (Building > load-balancing cluster) > > 2006/11/17, Sarah Walters <s.walters@xxxxxxxxxxxxx>: > > > > > The main problem is to build a shared storage that can > > > survive server > > > > > crashes, where mail will be stored. > > > > > > > > Use a SAN. > > > First of all, such SAN must be very reliable itself. > Second, it must > > > support some kind of global locking mechanism, so several > nodes can > > > use lock to protect file from simultaneous writing. > Third, Cyrus IMAP > > > must lock mailboxes, so several instances on different > server can work > > > with one mailbox without conflicts. Whether Cyrus IMAP > use locks or > > > assumes that he is the only one who access mail box, I > don't know. Can > > > it safely access one mailbox from different servers, I > don't know too. > > > > A good commercial SAN costs a fortune, but it is very > reliable. And did > > you want a *cluster* or a group of servers? A cluster > should operate as > > if it is a single host, and thus avoid the locking issues. > Have a look > > at Red Hat's clustering product for an example. If our cyrus > > installation was going to be clustered, RH cluster with a > SAN backend is > > what we would do. > > Yes, I need the cluster exactly. Have I lots of domains, I could store > mailboxes of each domain on separate server. But I have only one big > domain. So, I need to spread mailboxes on one domain across several > servers. And than I need very clever load-balancer that will send > request to server where particular mailbox is. I don't know such > balancers aware of mail system structure. I believe that Sun's mail server can do this, but if you lost a particular server you would lose the mailboxes on that server (or rather, would have to put up a new server connected to that part of the SAN storage). Why don't you look at throwing two beefy boxes at this problem in a hot-spare configuration? Have a single large box managing the mail and a heartbeat so that if one goes down the other immediately takes over its IP and just keeps going? You will lose anything that is actually in memory, but that shouldn't be an issue as long as you are using a SAN and immediately committing to disk rather than using a solution like MySQL. There is no need for load balancing here as far as I can tell, and what you lose in having to buy a chunkier server you will gain in reduced power consumption and associated data centre costs.
Yes, I know how failover cluster works. But what if one server (active) can't process such a load? Suppose, we plan to have 100 000 users working actively with mail. I understand that it is possible to use one monstrous server to take all of the load, but I am interested in load-balancing solution on relatively inexpensive servers. And what about slow anti-viruses for 100 000 users' mail? Or to use load-balanced front-ends connected to single SAN and connected to anti-virus load-balanced cluster? :-) --- 2006/11/17, Simon Matter <simon.matter@xxxxxxxxx>:
> 2006/11/17, Sarah Walters <s.walters@xxxxxxxxxxxxx>: >> > > > The main problem is to build a shared storage that can >> > survive server >> > > > crashes, where mail will be stored. >> > > >> > > Use a SAN. >> > First of all, such SAN must be very reliable itself. Second, it must >> > support some kind of global locking mechanism, so several nodes can >> > use lock to protect file from simultaneous writing. Third, Cyrus IMAP >> > must lock mailboxes, so several instances on different server can work >> > with one mailbox without conflicts. Whether Cyrus IMAP use locks or >> > assumes that he is the only one who access mail box, I don't know. Can >> > it safely access one mailbox from different servers, I don't know too. >> >> A good commercial SAN costs a fortune, but it is very reliable. And did >> you want a *cluster* or a group of servers? A cluster should operate as >> if it is a single host, and thus avoid the locking issues. Have a look >> at Red Hat's clustering product for an example. If our cyrus >> installation was going to be clustered, RH cluster with a SAN backend is >> what we would do. > > Yes, I need the cluster exactly. Have I lots of domains, I could store > mailboxes of each domain on separate server. But I have only one big > domain. So, I need to spread mailboxes on one domain across several > servers. And than I need very clever load-balancer that will send > request to server where particular mailbox is. I don't know such > balancers aware of mail system structure. The question here is what is "one big domain" exactly? How many users, what's the expected mailbox size (quota) and which usage pattern. That's what really matters here.
By one big domain I mean network domain. Consider gmail.com. You cannot make load-balancing by domain names. About 100 000 users with 100 mb mailboxes.
> Another way is to try to use something like GFS, constructed from > several servers. Each server will contain one portion of data and will > have Cyrus IMAP instance. But GFS will be mounted to each server, so > each Cyrus IMAP instance will see whole filesystem. Of course, here we > have same possible lock issues as with NFS. And we have no redundancy, > as I understand. > So, I need cluster for reliability to. I want to have each mailbox at > least on two servers (or to have shared storage upon two-nodes > failover cluster), so I can survive crash of any node (and not only of > disk system, that can be protected by RAID, but CPU crash, memory...) > with minimal recovery time. You may also search the list archives for some more info on the topic. There has been alot of discussion recently.
Please, tell me few keywords for search. Cyrus + GFS? ---- Cyrus Home Page: http://cyrusimap.web.cmu.edu/ Cyrus Wiki/FAQ: http://cyrusimap.web.cmu.edu/twiki List Archives/Info: http://asg.web.cmu.edu/cyrus/mailing-list.html
