Re: Disk performance under CURRENT

In message <20040521224729.680285D0A_at_ptavv.es.net>, "Kevin Oberman" writes:
>I just ran test of disk writing performance under V4 (STABLE) and V5
>(CURRENT) and was surprised at the difference.
>
>The test was simple and not at all rigorous. Just a dd bs=256k
>if=/dev/zero of=/dev/ad2. This is about the simplest way of dealing with
>a disk. No file system or anything else. Just raw data to the device.
>
>Under STABLE, I get an average of 25 MB/sec to the disk. Under CURRENT,
>it drops to 15 MB/sec. I did this because I had noted that it was now
>taking over an hour to backup my system disk (40 GB) when it was only
>taking 40 minutes when I was running V4.6. The STABLE system was built
>yesterday. The CURRENT system last Sunday.
>
>Any idea why this is so much slower? It looks to me like it must be in
>either geom or the disk driver.

GEOM is slower than 4-stable in a degenerate case like this, but it
sounds to me like there is something else involved here too.  Have
you removed WITNESS from your kernel ?

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