[mythtv-users] Hard Drive Performance

[Wander Winkelhorst]

On 3/31/06, Brian Wood <beww at beww.org> wrote:
>
> On Mar 30, 2006, at 10:33 PM, Martin Bene wrote:
>
> >> Since the OP's hdparm -tT numbers are way low it's obvious he has a
> >> problem not related to filesystem, although he might have those
> >> troubles as well.
> >
> >> /dev/hdc:
> >>  Timing cached reads:   1392 MB in  2.01 seconds = 692.30 MB/sec
> >>  Timing buffered disk reads:  188 MB in  3.00 seconds =  62.63 MB/sec
> >> [root at mythtv mythtv]# hdparm -tT /dev/hda
> >>
> >> /dev/hda:
> >>  Timing cached reads:   1368 MB in  2.00 seconds = 683.76 MB/sec
> >>  Timing buffered disk reads:  124 MB in  3.02 seconds =  41.12 MB/sec
> >
> > I don't see any indication of slow harddisks in these numbers -
> > "buffered disk reads" are OK.
> >
> > "cached reads" don't touch the disk hardware or interface at all, this
> > is cpu <-> memory bandwidth. Agreed, for a new system the
> > throughput is
> > rather pathetic.
> >
>
> I had assumed that "cached reads" were reading from the drive's
> internal cache, and would thus use the drives interface, but that was
> only an sssumption.

Well, ATA133 (The fastest parralel ATA to date) has only a maximum
throughput of 133 megabyte/sec, so there is no way you can do 683.76
MB/sec

>
> In any case, hdparm clearly showed that his hda drive was running in
> udma5 mode while the hdc drive was not, most likely due to the latter
> being on the same bus with an optical drive, and this clearly could
> and should be corrected.

Optical drives and hard discs can share a ATA bus without any slowdown
at all. The optical won't limit the hard disc to ATA33.

What will cause problems is using a 40 wire ATA cable instead of a 80
wire one. That WILL limit you to 33MB/sec speeds.

Allso, ATA is a 1 device-at-a-time protocol, so keep the devices that
you use the most at the same time on seperate busses.
So don't put the CDROM and the harddisc you are ripping to on the same
bus, and dont put the two hard discs on the same bus either

For best performance, buy each device (HD, CDROM, DVD, whatever) it's own bus.

Regards,
Wander.