load balancing at fastmail.fm

[Marten Lehmann]

Hello,

> Why do you need NFS?

because NFS is the only standard network file protocol. I don't want to 
load a proprietary driver into the kernel to access a SAN device.

> The whole point of a SAN is distributed access to storage after all :).

So where's the point? SANs usually have redundant network devices to 
access the redudant disk array behind it.

> It depends how much you trust your SAN.

Sure, but at some level you always have to trust to something.

> A SAN doesn't protect you if your filesystem decides to explode:

Well, there are inode based SANs and file based SANs. If I'm just 
splitting an inode based SAN, I could also use internal disks which give 
me more control. But with file based SANs I can actually store files 
(through NFS). And a lot of SANs offer the possibility to do snapshots 
or replicate their data filebased to another SAN. So you have a very 
high redundancy and availability. Me idea was, that Cyrus does lock and 
mmap indices and databases, but not the actual message-files. So these 
message files could be stored in the SAN with very high redundancy, 
whereas the metadata which needs to be mmaped remains on the blade with 
internal disks so in case of problems you could at least restore the 
messages from the SAN (and its snapshots if you accidentally deleted 
something) and rebuild the indices.


> I've heard horror stories about all the common Linux 
> filesystems and I've personally watched fsck.ext3 (supposedly the safest 
> option) unravel a filesystem, with thousands of entries left in 
> lost+found.

ext3 with journal? I have never experienced this.

> ZFS looks nice.

Well, but you are on your own because this project for linux is pretty 
young.

Regards
Marten