Frank Schwede, LSY wrote:
Now Im puzzled,
I wasnt aware of the fact you have to pay for an PAV license.
I didnt read the whole "story".
I was sure, that PAV is only an eckd-linux-driver bussiness, wich isnt
developed/released yet.
ianysmg,
but as far as I know, PAV is a licensed feature of the ESS that allows
you to have multiple subchannels (UCB's) to the same S/390 volume. While
the actual back-end disk can still serve only one request at a time,
your odds are good that the data you're after is in ESS cache already
and does not need access to the back-end. The Define Extent in the
channel program shows what part of the volume is affected by the
operation, and that allows the control unit to let one I/O request
overtake the other. To allow z/OS to take advantage of this, it gets two
subchannels leading to the same volume and has learned to drive the
other subchannel if one is busy.
With the LVM code in the SuSE SLES 8, Linux also knows how to drive
multiple subchannels to the same chunk of data. Like this:
Physical volume /dev/dasdi1 of vgb has 4 paths:
Device Weight Failed Pending State
# 0: 94:33 0 0 0 enabled
# 1: 94:37 0 0 0 enabled
# 2: 94:41 0 0 0 disabled
# 3: 94:45 0 0 0 disabled
Rob (need to ponder on the rest of the note)
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