Multiplexing, Multistreaming, And Multipathing; Multiplexing; Multistreaming; Multipathing - HP StorageWorks 12000 - Virtual Library System EVA Gateway Manual

do LUN mapping and masking 2) All hosts write to the library as a shared device. This involves
copies going on during prime backup or operational time on the hosts.
• Dedicated copy library for each virtual library -- This may be expensive with multiple virtual libraries.

Multiplexing, Multistreaming, and Multipathing

This section explains the concepts of Multiplexing,
of these technologies are useful for disk based backup devices and which are not recommended.

Multiplexing

This technology (sometimes called interleaving) is where multiple backup streams (from multiple servers)
are concurrently mixed together into a single tape drive (and thus a single tape cartridge). This is
commonly used for physical tape drives such as LTO where the speed of a single backup stream is
too slow to maximize the tape drive performance and you must run multiple concurrent streams together
into the drive to achieve full drive performance. However, this also means that restore performance
is severely affected because to restore a single backup stream (i.e., restore one server) the backup
application still has to read all of the intermixed data on the tape cartridge and then throw away the
data from the other backups. If you have five servers' backups multiplexed together on one tape
cartridge, you only get 20% restore performance when you restore one server.
Multiplexing is not recommended. When you have a disk backup device, you should disable
multiplexing on all backups going to the device because the main advantage of a disk backup device
is the ability to run many more concurrent backup streams than an equivalent physical library with
limited numbers of tape drives. For example, on the VLS you can create 32 virtual tape drives on
every Fibre Channel port and allow 32 non-multiplexed backup streams to be written concurrently to
each Fibre Channel port. This improves backup performance by allowing more backups to run in
parallel and improves restore performance because the backups are non-multiplexed. Disabling
multiplexing also improves deduplication efficiency and performance.

Multistreaming

This technology is where multiple objects in a backup job can be written concurrently to multiple tape
drives (each object going to a different drive). For example, if you have a file server with C:, D:, and
E: volumes, with multistreaming this could be concurrently written to three separate tape drives (C:
going to drive1, D: going to drive2, E: going to drive3). This increases the backup performance of
that server. Another example is a database backup where you may have multiple tablespaces or files
within the same database and these objects can be written in parallel to the tape drives, or some
database backup agents such as Oracle RMAN allow multiple streams even from one object (e.g.,
one database tablespace).
Multistreaming is recommended for disk based backup, particularly because many virtual tape drives
can be created thus allowing more concurrent streams to run from multistream backup jobs.

Multipathing

This technology uses two Fibre Channel paths from the backup server to the virtual tape library,
allowing for higher availability; for example, if you have dual SAN fabrics and wish to continue
operations even if one entire fabric fails. The VLS and D2D support the option of presenting any virtual
library device (changer or tape drive) on two Fibre Channel ports.
The main use of this is to present the virtual library changer device over two Fibre Channel ports
because the backup application must always be able to access the changer to perform any
backup/restore operations. Many enterprise backup applications (such as HP Data Protector, Symantec
36 Backup Solution Design Considerations
Multistreaming and Multipathing, and notes which