hdparm shows poor performance on cached reads for PATA drive

[Konstantin Svist]

John Summerfield wrote:
> Konstantin Svist wrote:
>> Konstantin Svist wrote:
>>> I have an older laptop (HP ze4400 series) with a PATA hard drive.
>>> When I check hdparm -T /dev/sda in Fedora 7 or 8, it shows me 
>>> performance of ~180MB/sec
>>>
>>> When I use a boot CD (gparted/clonezilla) to check the speed (by the 
>>> way, it uses the old style /dev/hdc, instead) - it tells me the 
>>> performance is upward of 400MB/sec
>>>
>>> The buffered speed seems about the same in either case at ~30MB/sec. 
>>> (I've tried enabling/disabling various settings via hdparm, while in 
>>> boot CD mode)
>>>
>>> Why is this happening and is there a way to fix it (without 
>>> reverting to /dev/hdc)?
>>
>>
>> *bump* since I got no replies from last time
>> Just ran another test: in F8, I get 123MB/s on cached reads, 28.55MB 
>> on buffered reads. When booted into Knoppix 5.1.0, cached reads say 
>> 210MB/s, and buffered reads fluctuate between 15MB/s and 20MB/s.
>
> For general performance, cached performance is pretty irrelevant, 
> you're still constrained to the bus speed at best, and the general 
> ability of the hardware (ATA motherboard electronics included) in 
> general.
>
> I don't have the foggiest idea of what an HP ze4400 is; depending on 
> its age your speed of 28.55MB is pretty good.
>

I agree that cached performance doesn't matter all that much, normally. 
However, it's a pretty large drop in performance - and I'm trying to 
figure out why it happened. I wouldn't be worried about it if it were 
off 5-10% - but it's just about HALF of the old value.
Also (and I'm not sure about this...) this might indicate some problem 
with latency (which *would* be pretty important, especially if it's this 
much).