Re: Can anyone explain this pgbench results?

Jim C. Nasby wrote:
> Well, the problem is that you're using RAID5, which has a huge write
> overhead. You're unlikely to get good performance with it.
Apparently. But I had no idea that the performance hit would be that big.

Running bonnie or copying a large file with dd show that the card can do 30-50 MB/sec. Running a large update on my postgresql database however, show a throughtput of ~ 2MB/sec, doing between ~ 2500 - 2300 writes/second (avarage). with an utilisation of almost always 100%, and large await times ( almost always > 700), large io-wait percentages (>50%), all measured with iostat.

> Also, it sounds like sda and sdb are not mirrored. If that's the case,
> you have no protection from a drive failure taking out your entire
> database, because you'd lose pg_xlog.
>
> If you want better performance your best bets are to either
> setup RAID10 or if you don't care about the data, just go to RAID0.
Because it is just my development machine I think I will opt for the last option. More diskspace left.

Groeten,

Joost Kraaijeveld
Askesis B.V.
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