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I'm not sure about popmail clients using it, but qmail's maildir is also
reportedly very safe with NFS v2. Although yeah, NFS v3 would be a
better alternative... and there are still speed issues with NFS under
linux (although some of the newer knfsd patches are getting pretty slick)
-Tymm
On Mon, 28 Jun 1999, Rob Thomas wrote:
> Date: Mon, 28 Jun 1999 11:49:06 +0000
> From: Rob Thomas <rob@xxxxxxxxxx>
> To: loc@xxxxxxxxxxxxxxxx
> Cc: linux-virtualserver@xxxxxxxxxxxx
> Subject: Re: LVS & Mail server ?
>
> loc@xxxxxxxxxxxxxxxx wrote:
>
> > I need this to convince my boss that LVS is THE SOLUTION for very
> > Scalable and High Available Mail/POP server. I have the intent to setup
>
> This is about the hardest clustering thing you'll ever do. Because of
> the constant read/write access's you -will- have problems with locking,
> and file corruption.. The 'best' way to do this is (IMHO):
>
> 1: NetCache Filer as the NFS disk server.
> 2: Several SMTP clients using NFS v3 to the NFS server.
> 3: Several POP/IMAP clients using NFS v3 to the NFS server.
> 4: At least one dedicated machine for sending mail out (smarthost)
> 5: LinuxDirector box in front of 2 and 3 firing requests off
>
> Now, items 1 2 -and- 3 can be replaced by Linux boxes, but, NFS v3 is
> still in Alpha on linux. I -believe- that NetBSD (FreeBSD? One of them)
> has a fully functional NFS v3 implementation, so you can use that.
>
> The reason why I emphasize NFSv3 is that it -finally- has 'real' locking
> support. You -must- have atomic locks to the file server, otherwise you
> -will- get corruption. And it's not something that'll happen
> occasionally. Picture this:
>
> [client] -- [ l.d ] -- [external host]
> |
> [smtp server]-+-[pop3 server]
> |
> [filesrv]
>
>
> Whilst [client] is reading mail (via [pop3 server]), [external host]
> sends an email to his mailbox. the pop3 client has a file handle on the
> mail spool, and suddenly data is appended to this. Now the problem is,
> the pop3 client has a copy of (what it thinks) is the mail spool in
> memory, and when the user deletes a file, the mail that's just been
> received will be deleted, because the pop3 client doesn't know about it.
>
> This is actually rather a simplification, as just about every pop3
> client understands this, and will let go of the file handle.. But, the
> same thing will happen if a message comes in -whilst the pop3d is
> deleting mail-.
>
> POP Client SMTP Client
> I want to lock this file <--
> I want to lock this file <--
> You can lock the file -->
> You can lock the file -->
> Consider it locked <--
> File is locked -->
> Consider it locked <--
> Ooh, I can't lock it -->
>
> The issue with NFS v1 and v2 is that whilst it has locking support, it's
> not atomic. NFS v3 can do this:
>
> POP Client SMTP Client
> I want to lock this file <--
> I want to lock this file <--
> File is locked -->
> Ooh, I can't lock it -->
>
>
> That's why you want NFSv3. Plus, it's faster, and it works over TCP,
> rather than UDP 8-)
>
> --Rob
>
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