Re: Horrible drive performance under concurrent i/o jobs (dlh problem?)

[Denis Vlasenko]

On 18 December 2002 17:06, Torben Frey wrote:
> Hi list readers (and hopefully writers),
>
> after getting crazy with our main server in the company for over a
> week now, this list is possibly my last help - I am no kernel
> programmer but suscpect it to be a kernel problem. Reading through
> the list did not help me (although I already thought so, see below).
>
> We are running a 3ware Escalade 7850 Raid controller with 7 IBM
> Deskstar GXP 180 disks in Raid 5 mode, so it builds a 1.11TB disk.
> There's one partition on it, /dev/sda1, formatted with Reiserfs
> format 3.6. The Board is an MSI 6501 (K7D Master) with 1GB RAM but
> only one processor.
>
> We were running the Raid smoothly while there was not much I/O - but
> when we tried to produce large amounts of data last week, read and
> write performance went down to inacceptable low rates. The load of
> the machine went high up to 8,9,10... and every disk access stopped
> processes from responding for a few seconds (nedit, ls). An "rm" of
> many small files made the machine not react to "reboot" anymore, I
> had to reset it.

Can you provide solid numbers (say Mb/s) of single dd's of varying
size? Of concurrent dd's? etc...

> When I am working all alone on the disk creating a 1 GB file by
> time dd if=/dev/zero of=testfile bs=1G count=1
> results in real times from 14 seconds when I am very lucky up to 4
> minutes usually.
> Watching vmstat 1 shows me that "bo" drops quickly down from rates in
> the 10 or 20 thousands to low rates of about 2 or 3 thousands when
> the runs take so long.

Yes, and provide us with vmstat, top, cat /proc/meminfo output
and the like!
--
vda