Re: [Fwd: Optimizing Squid performance]

Thanks for the illustration on RAID 5. That resolved as a not to do, what
else should I tweak to achive my objective?

Athanasios Kourousis
Unifon - T.C.P. S.A.
akouroussis@unifon.com.ar

Robert Collins wrote:

> > -----Original Message-----
> > From: Athanasios Kouroussis [mailto:akouroussis@unifon.com.ar]
> > Sent: Tuesday, 8 August 2000 8:10 AM
> > To: Duane Wessels
> > Cc: squid-users@ircache.net
> > Subject: Re: [Fwd: Optimizing Squid performance]
> >
> >
> > Thanks for the prompt reply:
> >
> > 1) Top or free report 3 of 512Mb of physical memory free.
> > Only 40Mb of swap
> > space used.
> > 2) Why do not use raid if it controlled by hardware. I can
> > understand not
> > using software RAID or RAID 5 with a poor controller but the
> > RAID controller
> > of this box is a Smart-2 3200. Anyway, what do you
> > recommend. How should I
> > set up the partitions (size, fs, etc) for max perf. Any
> > other, squid related
> > parameters I should tweek?
>
> RAID 5 incurs a read-write overhead regardless of software or hardware
> implementation. It can be up to 1/4 the speed of a striped no-parity
> configuration.
>
> The reason is that for every stripe, a write anywhere to the stripe
> requires:
> A) read the stripe block BLOCK-A(up to 64K on most controllers) that
> contains logical blocks that are being written to.
> B)read the parity stripe block for that stripe. (same size as A)
> C) remove the old BLOCK-A from the parity value
> D) add the new BLOCK-A to the parity value
> E) write the new BLOCK-A to disk
> F) write the new parity block to disk.
>
> As you can see a single write of 2K (say a small.gif) will require 2
> head reads (1 each on two of the array disks) and 2 writes (back to the
> same sector).
>
> Whereas mirroring or striping no-parity require only two writes
> (mirroring) or 1 write (no parity striping).
>
> So we won't use RAID 5 for high-performance applications.
>
> For cache data where you probably don't care about the data itself,
> having multiple independant disks means that if a failure occurs, squid
> can stop using that disk rather than you losing a full stripe, and you
> don't need to pay the 100% overhead of mirroring.
>
> Rob
>
> > 3) May that is the reason.. I will check it and let you know.
> >
> > Thanks,
> >
> > Athanasios Kouroussis
> > Unifon - T.C.P. S.A.
> > akourousssis@unifon.com.ar
> >
Received on Mon Aug 07 2000 - 18:52:45 MDT