Re: Higher than expected disk write(2) latency

[Arjan van de Ven]

On Thu, 10 Jul 2008 15:41:46 +0200
Martin Lucina <mato@xxxxxxxxxx> wrote:

> chris.mason@xxxxxxxxxx said:
> > Is NCQ enabled on the drive?  The basic way to fix this is to have
> > multiple requests in flight, which isn't going to happen on sata
> > with the cache off and with ncq off.
> 
> ata1: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
> ata1.00: ATA-7: Hitachi HDS721616PLA380, P22OAB3A, max UDMA/133
> ata1.00: 321672960 sectors, multi 0: LBA48 NCQ (depth 31/32)
> ata1.00: configured for UDMA/133
> 
> I'm assuming the above indicates NCQ is enabled.
> 
> We'll try running the tests tomorrow with different i/o schedulers and
> report back.


another thing to try is using AHCI mode instead; AHCI tends to be
higher performance

(and.. for fun try to run latencytop during a run, to see if maybe
there are unsuspected delay causes)

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