On real hardware, the READ_COUNT will give you the address of the record
whose key is being compared by the next CCW. It's a sequence that is
heavily used in searches of non-indexed VTOCs.
Rick
------------------------------------------
shai hess wrote:
Yes, I know it and I support it.
But be aware that I can not see the result of the READ_COUNT because I take
control before the IO is really done to the real device.
Shai
On Mon, Nov 1, 2010 at 12:27 PM, Rick Fochtman <[email protected]> wrote:
---------------------------------------<snip>-----------------------------------
A few words on replication.
The standard replication is sending CCWS to all controller which
have mirrors disks. Sometime controller send data to other controller to
sync the data between all of them.
In this process each controller emulates the CCWS and by that create the
same data as the source disk. In this case the search key is very easy to
implement.
MFNetDisk because of the slow media of TCP do something else. It is
analyze
the CCW in memory without accessing the source disk data. That is why it
is
hard to process the search key without access the data in the disk. After
process the CCW it is decide what tracks need to be ReSync in the mirrors
of
the source disks. This process is complicate process especially for search
key CCW. Using this processing, MFNetDisk never block the real disk but
the
minus is that this is ASync processing meaning that if there is crash in
MF,
the mirror may be not fully Sync with the source disk. the MFNetDisk
replication can be good if you want to create Sync point or backup of the
real disk in specific time where you can validate that the process of
ReSync
is done completely without updating the source disks for short time until
the ReSync is totally over. This is called Sync Point where the mirrors is
fully Sync with the real disk.
About the MFNetDisk emulation. Each CCW is sent to the PC which access the
data in the emulate disks and easily can process any CCW include serach
key
and all other CCWS.
-------------------------------------------<unsnip>-------------------------------------
Shai, it's entirely acceptyable to use a READ COUNT CCW before the SEARCH
KEY HIGH-OR-EQUAL CCW.
READ COUNT
SEARCH KEY HIGH-OR-EQUAL
TIC *-16 (Back to the READ COUNT
READY DATA (or WRITE DATA, as needed)
Rick
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