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SubjectRe: SATA buffered read VERY slow (not raid, Promise TX300 card); 2.6.23.1(vanilla)
On 12/30/2007 12:06 AM, Linda Walsh wrote:
> I needed to get a new hard disk for one of my systems and thought that
> it was about time to start going with SATA.
>
> I picked up a Promise 4-Port Sata300-TX4 to go with a 750G
> Seagate SATA -- I'd had good luck with a Promise ATA100 (P)ATA
> and lower capacity Seagates and thought it would be a good combo.
>
> Unfortunately, the *buffered* read performance is *horrible*!
>
> I timed the new disk against a 400GB PATA and old 80MB/s SCSI-based
> 18.3G hard disk. While the raw speed numbers are faster as expected,
> the linux-buffered read numbers are not good.
>
>
> sda=18.3G on 80MB/s SCSI
> sdb=the new 750GB on a 3Gb SATA w/NCQ.
> hdf=400GB PATA on an ATA100 Promise card
>
> I used "dd" for my tests, reading 2GB on a quiescent machine
> that has 1GB of main memory. Output was to dev null. Input
> was from the device (not a partition or file), (/dev/sda, /dev/sdb
> and /dev/hdf). BS=1M, Count=2k. For the direct tests, I used
> the "iflag=direct" param. No RAID or "volumes" are involved.
>
> In each case, I took best run time out of 3 runs.
>
> Direct read speeds (and cpu usage):
> dev speed cpu/real %
> sda 60MB/s 0.51/35.84 1.44
> sdb 80MB/s 0.50/26.72 1.87
> hdf 69.4MB/s 0.51/30.92 1.68
>
>
> Buffered reads show the "bad news":
> dev speed cpu/real %
> sda 59.9MB/s 20.80/35.86 58.03
> sdb 18.7MB/s 16.07/114.73 14.01 <-SATA extra badness
> hdf 69.8MB/s 17.37/30.76 56.48
>
> I assume this isn't expected behavior.
>

Try the PATA driver for the parallel ATA drive to see if it
has the same behavior.

Reboot before each test (or use drop_caches.)

hdparm should mostly work for reading drive settings but not for
writing them...


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