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Subject: Re: high capacity configuration nightmares
From: Wietse Venema (wietseporcupine.org)
Date: Thu Oct 26 2000 - 13:30:51 CDT

Pere Camps:
> time ./smtp-source -s 50 -l 10000 -m 1000 -c -f meme.com -t
> deletemelocalhost localhost
>
> syslog: async
> filesystem: sync
>
> machine: dual pentium III, 733 Mhz, .5 GB RAM, compaq smart
> array RAID 5 controller.
>
> maximum smtp connections in postfix: 300
>
> sessions time
> -------- ----
> 50 2m10s
> 100 1m39s
> 150 1m20s

With 20 messages/second, that is twice as slow as my measurements
with single disk SCSI system.

For first-hand experiences, type "raid 5 performance" into google
and see for yourself why RAID 4/5 write performance sucks so badly.

RAID 5 write performance sucks, especially for random writes. And
that is exactly what Postfix spends all its time waiting for.

RAID 5 random write performance is slower than with a single-disk
architecture, because to write a data block, RAID 5 also has to read
then update a parity block. read+update is slower than just write.

RAID 5 is OK for read-mostly stuff like web servers. Not for mail.

        Wietse