Re: Slow disk performance (was: Re: install help 6400/200)
On 29 Jul, this messageom Rogerio Saran echoed through cyberspace:
> Michael, thank you for the corrections.
You're welcome :-)
> I have some comments may also be
> useful for those considering an old PowerMac as a Debian platform.
I hope some are inspired by your comments. I run Woody myself on a
7600/G3/300, and all I can say is it performs beautifully for a 7-year
old Computer :-)
>> Errmm.. no, the 9x00 series have no 64-bit slots. Those were the
>> first-generation PCI machines. You're a generation too far :-).
> You are absolutely right, only 32 bit PCI. I am sorry for the imprecise
> comment. I got confused because for most high performance peripherals is
> recommended to use slots 1 and 4. These are the first on each of the
> 9500 PCI buses, and ensure better throughput (I do not know the reason.)
Maybe arbitration? Although I thought I remebered reading that all PCI
devices share equal arbitration priorities (with the exception of
GrandCentral)...
>>>Just add a good SCSI card (Ultra-2 LVD or Ultra160) and a
>>>newer disk to see real (not bus nominal) transfer speeds of 25-40 Mb/s.
>>
>> Or an IDE card, for that matter. I get close to 15 MB/s on a (now rather
>> old) 10 Gig Maxtor 7200 rpm disk with a Promise Ultra/66.
>
> You are right. I did not mention IDE because it usually blocks the
> system for too much time during disk operations.
>
> I have no experience with IDE on PowerMacs, but on PCs a single
> large-file copy is a sure way to slow down the system to a crawl. This
> is not a problem on most workstations, but for a server with more then
> minimal traffic it may be a real concern.
Yeah, I get the 'freezes' a lot on my TiBook (which is obviously
IDE...). It's worst at disk wake-up time, but that's kind of expected.
Reads or writes of large blocks also cause the same symptom...
> Of course those who can afford Ultra2 or Ultra160 mirrored-controller
> striped-disk systems will experience stunning results for any kind of
> disk usage.
I have some experience with Ultra160 on a Dell server (1 Gig PIII;
nothing fancy...); its 'perceived' performance is rather fabulous
compared to similar CPU desktop systems.
> I sounds like madness, but an 9500 can handle mirrored controllers on
> its dual PCI buses. Some performance addicted have tried 4-disk setups
> where each controller handle a striped volume set with stunning results!
Cool :-)
> I am trying to reach these performance levels on my 8500, but I am still
> doing reserch on Linux (Debian) compatible hardware.
Try to get a controller that will do 'Memory Write and Invalidate' and
'Memory Read Multiple' DMA transfers over the PCI bus; those will give
you maximum performance. No idea though which ones will indeed support
those... Maybe have a look at the driver source codes.
Cheers
Michel
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