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    SubjectRe: max request size 1024KiB by default?
    On Sat, Jul 24, 2004 at 06:58:02PM -0400, Lee Revell wrote:
    > On Sat, 2004-07-24 at 07:27, Rudo Thomas wrote:
    > > > HD info:
    > > > /dev/hdc:
    > > >
    > > > Model=Maxtor 6Y160P0, FwRev=YAR41BW0, SerialNo=Y44K8TZE
    > > > Config={ Fixed }
    > > > RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=57
    > > > BuffType=DualPortCache, BuffSize=7936kB, MaxMultSect=16, MultSect=16
    > > > CurCHS=4047/16/255, CurSects=16511760, LBA=yes, LBAsects=268435455
    > > > IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
    > > > PIO modes: pio0 pio1 pio2 pio3 pio4
    > > > DMA modes: mdma0 mdma1 mdma2
    > > > UDMA modes: udma0 udma1 udma2 udma3 udma4 udma5 *udma6
    > > > AdvancedPM=yes: disabled (255) WriteCache=enabled
    > > > Drive conforms to: (null):
    > >
    >
    > Your disk controller must not support that. It looks like the default
    > is 1024KiB or whatever the max your controller supports is:

    For drives smaller than 128GiB the "48-bit Address feature set" is optional,
    hence many older drives do not support it (since the old 28-bit LBA
    addressing is suffient).

    With 28-bit addressing the number sectors which can be transferred
    in one request is limited to 256. Linux 2.4 limited this further
    to 128 (i.e. 64KiB). With 48-bit addressing up to 2^16 sectors
    could be transferred in one request, but Linux 2.6 puts an arbitrarily
    chosen limit of 1024KiB on it.

    'hdparm -I /dev/hda' will tell you whether your drive supports
    48-bit addressing:

    Commands/features:
    Enabled Supported:
    * 48-bit Address feature set

    For full details see the ATA/ATAPI-7 spec at http://www.t13.org/.

    Johannes
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