swamped mail relays - suggestions

[Greg Matthews]

I'm running three mail relays served round-robin by DNS. Over the last
month these have started to struggle to cope with the load.

I've installed a caching DNS server on one and it may have a small
effect offsetting the RBL lookups but it's too small to be definite. All
3 have a DNS server close by on the local network.

I'm thinking about changing the file system used to hold the mqueue.in
directory. At the moment, it is ext3. Do people have recommendations for
this? I'm running with an older redhat kernel so XFS isnt an immediate
option but ReiserFS is.

At the moment I have around 10000 emails in the incoming queue on each
machine and typical iostat numbers look like:

Device:    rrqm/s wrqm/s   r/s   w/s  rsec/s  wsec/s    rkB/s    wkB/s avgrq-sz avgqu-sz   await  svctm  %util
/dev/sda     0.80 621.80 12.00 232.00  104.00 6873.60    52.00  3436.80    28.60   964.72  394.43   3.07  74.80
/dev/sda1    0.00   0.00  0.00  0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
/dev/sda2    0.80 621.80 12.00 232.00  104.00 6873.60    52.00  3436.80    28.60   964.72  394.43   3.07  74.80
/dev/sdb     0.00 620.40  8.80 233.40   70.40 6873.60    35.20  3436.80    28.67   967.70  398.60   3.13  75.80
/dev/sdb1    0.00   0.00  0.00  0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
/dev/sdb2    0.00 620.40  8.80 233.40   70.40 6873.60    35.20  3436.80    28.67   967.70  398.60   3.13  75.80

I'm not exactly expert on interpreting this but the await numbers look
high as does the queue size (I've just seen it at 951).

The relays are using md to create a raid1 mirror of two scsi disks,
could the md be a bottleneck too?

Each box has dual 2.8GHz Xeons with hyperthreading turned on - is HT a
winner or should I turn it off?

Perhaps I just need more/faster hardware?

Any comments and suggestions most welcome.

GREG
--
Greg Matthews           01491 692445
Head of UNIX/Linux, iTSS Wallingford

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