Re: [PATCHES] COPY FROM performance improvements

Joshua,

On 7/22/05 10:11 AM, "Joshua D. Drake" <jd(at)commandprompt(dot)com> wrote:
> The database server is a PE (Power Edge) 6600
>
> Database Server IO:
>
> [root(at)master root]# /sbin/hdparm -tT /dev/sda
>
> /dev/sda:
> Timing buffer-cache reads: 1888 MB in 2.00 seconds = 944.00 MB/sec
> Timing buffered disk reads: 32 MB in 3.06 seconds = 10.46 MB/sec
>
> Second Database Server IO:
>
> [root(at)pq-slave root]# /sbin/hdparm -tT /dev/sda
>
> /dev/sda:
> Timing buffer-cache reads: 1816 MB in 2.00 seconds = 908.00 MB/sec
> Timing buffered disk reads: 26 MB in 3.11 seconds = 8.36 MB/sec
> [root(at)pq-slave root]#

Can you post the "time dd if=/dev/zero of=bigfile bs=8k count=500000"
results? Also do the reverse (read the file) with "time dd if=bigfile
of=/dev/null bs=8k".

I think you are observing what we've known for a while, hardware RAID is
horribly slow. We've not found a hardware RAID adapter of this class yet
that shows reasonable read or write performance. The Adaptec 2400R or the
LSI or others have terrible internal I/O compared to raw SCSI with software
RAID, and even the CPU usage is higher on these cards while doing slower I/O
than linux SW RAID.

Notably - we've found that the 3Ware RAID controller does a better job than
the low end SCSI RAID at HW RAID support, and also exports JBOD at high
speeds. If you export JBOD on the low end SCSI RAID adapters, the
performance is also very poor, though generally faster than using HW RAID.

- Luke