Re: Robustness
On Fri, 26 Nov 1999, Chris Wagner wrote:
>>I want to replicate a pop mailboxes but I don't know how.
>
>Set up POP service on both machines. Map both their IP addresses to the POP
>server name. Then use rsync to make sure the mail spools match. This is a
>simple solution and there are problems.
>
>1) Both machines have to have the same user accounts unless you go with qpop
>or something
>2) If one dies, the R-R DNS will give out the dead address 50% of the time
>
>A better solution is to setup two POP machines which mount the mail spool
>off a third NFS machine. This NFS server should be RAID-5. Between your
>users and these POP machines put a firewall/proxy. It is this proxy that
>will split up the traffic between them and know if one dies.
RAID-5 is good if you're on a budget. However performance for writes is poor
(try running Bonnie or Bonnie++ on a RAID-5 filesystem and compare to RAID-10,
or RAID-1). If you're in the situation where you need more than one server
in case of a crash then you probably don't need to save money on RAID-5.
Also as 72G SCSI drives are available you can have 72G of RAID-1 storage at
minimal effort.
For a mail spool writes will probably equal reads so write performance counts.
>But that may be overkill. Really, your best bet is to just use rsync to
>keep a backup copy of the mail spool on another harddrive and if the machine
>dies, stick the backup mail spool in a "hot spare" POP server. Having the
>kind of fault tolerant POP service you're thinking of is a non-trivial exercise.
If you have a small amount of data then you probably don't need this. If you
have a lot then rsync really won't cope. If you have 20G of data then rsync
will probably take 20 minutes to run.
The cheapest solution for redundancy of file servers is dual-attached SCSI.
Of course making sure that machine A is dead before machine B mounts the
drive is non-trivial...
--
Electronic information tampers with your soul.
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