Messages in this thread |  | | Date | Sun, 15 Jul 2001 10:39:52 -0700 | From | Jonathan Lundell <> | Subject | Re: [PATCH] 64 bit scsi read/write |
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At 5:10 AM +1200 2001-07-16, Chris Wedgwood wrote: >On Sat, Jul 14, 2001 at 09:45:44AM +0100, Alan Cox wrote: > > As far as I can tell none of them at least in the IDE world > >Can you test with the code I posted a hour or so ago please?
AC's comment was about whether the drive's cache would be written out on power failure, which is another issue, a little harder to test (and not easily testable by writing a single sector). I raise the related question of what happens to the write cache on a bus reset on SCSI drives.
>I ask this because I tested writes to: > > -- buffered devices > > -- ide with caching on > > -- ide with caching off > > -- scsi (caching on?) > >To a buffered device, I get something silly like 63000 >writes/second. No big surprises there (other than Linux is bloody lean >these days). > >To a SCSI device (10K RPM SCSI-3 160 drive), I get something like 167 >writes/second, which seems moderately sane if caching is disabled.
My impression, based a a little but not much research, is that most SCSI drives disable write caching by default. IBM SCSI drives may be an exception to this.
>To a cheap IDE drive (5400 RPM?) with caching off, I get about 87 >writes/second. > >To the same drive, with caching on, I get almost 4000 writes/second. > >This seems to imply, at least for my test IDE drive, you can turn >caching off --- and its about half as fast as my SCSI drives which >rotate at about twice the speed (sanity check). > >IDE drive: IBM-DTTA-351010, ATA DISK drive >SCSI drive: SEAGATE ST318404LC
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