[wplug] Re: Thoughts & Considerations for email server (versus a web server)

[Bryan J. Smith]

"Bryan J. Smith" <thebs413 at yahoo.com> wrote:
> If you have largely reads, I utterly agree.
> If you have writes, I haven't seen a software RAID-5 implementation
> on a PC that could sustain more than 25-30MBps.  It's a limit of
> the CPU-memory interconnect -- it's just not possible to feed
> data fast enough into the CPU (the CPU itself can do GBps of XOR).

Last time I pegged it (at roughly 2 sigma), 97% of Linux consultants
are doing web servers.  For web servers, software RAID-5 is
_just_fine_.  No need for a hardware RAID controller at all.

That's because they are a combination of doing 99% reads, and in the
case of dynamic content, the system is processor-bound, not
I/O-bound.  So there is not only plenty of "room" for the added I/O
of software RAID-5, but writes are so infrequent that 20MBps bursts
are all that are required.  The kernel can more than schedule that
without any impact.

The only remaining issue for that then becomes hot-swap -- of which,
I highly recommend SAS/SCSI, as hot-swap ATA support is rather
limited.


-- 
Bryan J. Smith   Professional, Technical Annoyance
b.j.smith at ieee.org    http://thebs413.blogspot.com
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