HP 3000 Manuals HP 3000 Manuals
Interleaving Files
Interleaving gives you the capability of simultaneously reading
information from different files on multiple disk drives and storing the
accessed information on the backup device in a single operation. It also
allows you to match a slow input device (for example, a disk drive), with
a fast backup device (for example, a streaming tape drive or a digital
audio tape). This effectively increases the input rate. By varying the
number of concurrent input operations, the effective input rate can be
matched with the output rate. This allows the backup to execute at the
speed of the output device.
When you store files in interleave format, the following happens:
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1. The set of files to your backup device(s) is partitioned.
2. The files are copied. STORE can (depending upon file
characteristics) access several files at the same time.
3. The files are interleaved on the same piece of media to ensure
that your backup device(s) operate at full speed.
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Interleave format significantly reduces the time necessary to store a
large set of files, such as when performing a full system backup. It
merges the stream of data from multiple files on separate disks into a
single stream of data sent to the backup device or devices. If
necessary, STORE processes files out of sequence to keep backup devices
operating efficiently (refer to "Interleave Format Tapes" in appendix C
for format).
Interleave format is most efficient when your file set is evenly spread
across two or more system disks. Use sequential devices or parallel
devices alone when the set of files to store is smaller and less evenly
distributed, for example when doing a partial backup.
To store files in interleave format, use the INTER parameter of the STORE
command. For example,
FILE T;DEV=TAPE
STORE @.OPERATOR.SYS;*T;INTER
When these files are restored, RESTORE automatically recognizes the
interleave format and restores the files properly.
Using the STORESET and INTER parameters together improves backup time on
large systems. (Refer to "Storing to Multiple Devices," in chapter 2,
for more information on the STORESET parameter.) For example, the
following STORE command uses both parallel device pools and interleaving
to minimize backup time:
STORE @.@.@;;SHOW=OFFLINE;&
STORESET=(*T,*T),(*T,*T);INTER