During simultaneous-write operations, a client
session
requires a mount point for each sequential-access storage pool to
which data is written. Transactions fail if the number of mount points
that are required for a client session is insufficient.
About this task
Give careful consideration to the number
of mount points
that are available for a simultaneous-write operation. A client session
requires a mount point to store data to a sequential-access storage
pool. For example, if a storage pool hierarchy includes a sequential primary
storage pool, the client node requires one mount point for that pool
plus one mount point for each copy storage pool and active-data pool.
Suppose,
for example, you create a storage pool hierarchy like the hierarchy
shown in Figure 1.
DISKPOOL is a random-access storage pool, and TAPEPOOL, COPYPOOL1,
COPYPOOL2, and ACTIVEDATAPOOL are sequential-access storage pools.
For each client backup session, the client might have to acquire four
mount points if it has to write data to TAPEPOOL. To run two backup
sessions concurrently, the client requires a total of eight mount
points.
To indicate the number of mount points a client can
have, specify a value for the MAXNUMMP parameter
on the REGISTER NODE or UPDATE NODE commands.
Verify the value of the MAXNUMMP parameter and,
if necessary, update it if you want to enable the simultaneous-write
function. A value of 3 for the MAXNUMMP parameter
might be sufficient if, during a client session, all the data is stored
in DISKPOOL, COPYPOOL1, COPYPOOL2, and ACTIVEDATAPOOL.
If the
number of mount points that are required for a client session exceeds
the value of the client
MAXNUMMP parameter, the
transaction fails. If the transaction involves an active-data pool,
all the active-data pools are removed from the active-data pool list
for the duration of the client session, and the client tries the operation
again. If the transaction involves a copy storage pool, the setting
of the
COPYCONTINUE parameter in the storage
pool definition determines whether the transaction is tried again:
- If the value of the COPYCONTINUE parameter
is NO, the client does not try the operation again.
- If the
value of the COPYCONTINUE parameter
is YES, all the copy storage pools are removed from the copy
storage pool list for the duration of the client session. The client
tries the operation again.
Restrictions: - The setting of the COPYCONTINUE parameter
does not affect active-data pools. If a write failure occurs for any
of active-data pools, the server stops writing to the failing active-data
pool for the remainder of the session, but continues storing files
into the primary pool and any remaining active-data pools and copy
storage pools. The active-data pool list is active only for the life
of the session and applies to all the primary storage pools in a particular
storage pool hierarchy.
- The setting of the COPYCONTINUE parameter
does not affect the simultaneous-write function during server import.
If data is being written simultaneously and a write failure occurs
to the primary storage pool or any copy storage pool, the server import
process fails.
- The setting of the COPYCONTINUE parameter
does not affect the simultaneous-write function during migration.
If data is being written simultaneously and a write failure occurs
to any copy storage pool or active-data pool, the failing storage
pool is removed and the data migration process continues. Write failures
to the primary storage pool cause the migration process to fail.