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Re: Slow disk performance (was: Re: install help 6400/200)

The standard internal SCSI bus on OldWord PowerMacs is quite slow
for today standards, with 10 Mb/s of nominal bandwitdh.

To make it worse factory installed hard disks where specially slow.
Tipical sustained transfer read ates under MacOS are in the 3-5 Mb/s
range. With multi-tasking OSes this may be even worse as the CPU is
shared between io wait and active tasks.

I remeber spending 4 hours to format 1 Gb disks with MacOS utilities in
1992. The first time I set-up a 9500 it took 1 hour to format its
2 Gb factory-installed hard drive. Last week I began to configure a 8500
with an Apple internal 2Gb drive, and it took 50 minutes on formatting.

This same machine supports a ten-fold increase in transfer rates using
newer SCSI appliances. The 9500 provides 6 PCI slots and two of them are
64 bit wide. 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.

Some disk controllers even provide striping features, letting you read
file fragments in parallel from different physical disks. Some setups
deliver sustained 130 Mb/s read data rates.

On memory and crashes: OldWorld PowerMacs are very sensitive to memory and
bus speed. I am not sure but your machine bus probably runs at 45 MHz.
Defective memory chips may fail even in standard speed, and certainly
fail if you overclock the bus. Just forget about using your old memory,
give the dimms away for someone with a PowerMac with lower bus speed.

The 9500 has an additional problem, because its 512 Kb L2 cache is soldered
in the mainboard and can't be replaced, but usually it is a good quality


> On Jul 25 2002, Trench Shoring wrote:
> > Install takes about a week to format the entire 10G drive. I must be
> > missing a basic howto. Is there a www site or tips on installing to
> > this not so ancient Mac?
>  First of all, I would like to point out that I don't know
>  enough about macs as some here do, especially about older macs
>  (finding macs in my country is not the easiest thing).
>  Anyway, I have a PowerMac 9500/180MP (my uncle's) and the disk
>  performance is quite low compared to other computers that I
>  know.
>  In fact, it is surprisingly slow as the disk in use is SCSI
>  and I see that all the computer almost freezes whenever there
>  is any disk access. I am using an SMP 2.4.x-benh kernel, but
>  it seems that this behaviour is OS-agnostic, as I see it occur
>  at least with MacOS X (installed via XPostFacto) and Linux. I
>  have little experience with MacOS 9 to judge if this slowdown
>  is still there, but I would guess so.
>  I would even dare to say that the disk seem to be this
>  machine's bottleneck.
>  I don't know if the problem is a configuration problem or if
>  it is something intrinsic to this system. I would appreciate
>  if anybody could help me here. I am not in front of this mac
>  right now, but I can get all the details needed for debugging
>  the situation (or understanding if this is a limitation of
>  this computer).
>  I guess that my reply partially replies to the above poster.
>  OTOH, that powermac has a 3G drive and while it does take some
>  time to ext2-format the drive (scanning for bad blocks) it
>  takes something like, say, 1 hour, but, NOT a whole week.
> > YDog; System crashes during partitioning.
>  I had strange things happenning to this mac (like LinuxPPC Q4,
>  Debian potato and Yellowdog Linux 2.0 dying during their
>  installs -- they were current when I tried them), until I
>  exchanged both the hard drive and the system's memory (both
>  were defective).
>  The memory problems were particularly fun, as I got all sorts
>  of un-deterministic behaviour from the computer.
>  Well, I hope this helps and I also hope someone can help me.
>  :-)
>  []s, Roger...
> P.S.: Which rates am I expected to see with a SCSI drive on the PMac?
> I remember that I get low rates whenever I use "hdparm -tT /dev/sda",
> but, as I said earlier, I'm not with the mac here to give exact
> figures -- I can provide them later, of course.
> --
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
> Rogério Brito - linuxconsult@yahoo.com.br - http://www.ime.usp.br/~rbrito
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
> --
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Rogério Saran

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