strange performance dip shown by iozone

[Dmitry Alyabyev]

On Thursday 19 February 2004 00:29, mi+mx at aldan.algebra.com wrote:
> Hello!
>
> I'm trying to tune the amrd-based RAID5 and have made several iozone
> runs on the array and -- for comparision -- on the single disk connected
> to the Serial ATA controller directly.
>
> The RAID-based FS was newfs-ed with ``-b 65536'', as it is intended to
> store very large files. The single-disk FS was newfs-ed with defaults.
>
> No softupdates were enabled on either, since those seem to degrade iozone
> results slightly (iozone reads/writes a single file anyway).
>
> The filesystems displayed different performance (reads are better with
> RAID, writes -- with the single disk), but both have shown a notable dip
> in writing (and re-writing) speed when iozone used the record lengthes
> of 128 and 256. Can someone explain that? Is that a known fact? How can
> that be avoided?
>
> The machine is an amd64 running a fresh -current. The disks are 200Gb
> SATAs. RAID5 consists of 6 of them.

which stripe size of RAID5 did you use ?

-- 
Dimitry