How To:Write to Multiple Volumes in Parallel
Amanda can write to multiple volumes in parallel, saving a lot of time.
This is useful if you write to more than one volume in a run and the changer have more than one drive.
- A different dle is sent to each volumes.
- All parts of a dle are contiguous on a volume.
- If splitting is enabled and a volume get EOT, the next part of the dle can be on any volume, not necessarily on a new volume.
- The use of holding disk is still recommended, it allow more dumps in parallel and many dles are not fast enough to stream a tape drive.
- If a drive is not available at the beginning of the run, amanda will not use it, it doesn't poll for available drive.
Advantage
- Writing to many volume in parallel save times.
- Can do more than one dump direct to tape in parallel.
Disadvantage
- Require a more powerful server to be able to stream multiple drives.
- Performance can be worse if the server can't stream all the drives.
Requirements
- A Changer with the new changer API must be used.
- More than one drive must be defined.
Global Configuration
The taper-parallel-write config option must be set to the number of volume amanda can write to in parallel.
In amanda.conf:
taper-parallel-write 2
Changer Configuration
How to defined multiple drives:
- chg-disk: Nothing to do, an infinite number of drive is already available.
- chg-multi: Nothing to do, all drives are already defined.
- chg-ndmp: Define all drives with the tape-device property.
- chg-robot: Define all drives with the tape-device property.
- chg-single: Impossible to do, only one drive is available.
Examples
- chg-disk
taper-parallel-write 2 tpchanger "chg-disk:/path/to/vtapes"
- chg-robot
taper-parallel-write 2
define changer hp-robot {
tapedev "chg-robot:/dev/sg1"
property "tape-device" "0=tape:/dev/nst0"
property append "tape-device" "1=tape:/dev/nst1"
}
tpchanger "hp-robot"