Split or Spanning Dumps across Multiple Tapes

This article is for Amanda Enterprise (AE)

What is it

Split Dumps or Dump Spanning enables a single dump to be span across multiple volumes or tapes. This permits you to have Disk List Entries (DLEs) larger than any single tape you may have, as well making more efficient use of tape space under certain circumstances.

It works by splitting a large dump file into smaller chunks of a configurable size before writing to tape, allowing AMANDA to regard each individual piece as a dump file in its own right and following “tape full” semantics as it would a normal dump.

Configuration / How-to

To configure a backup to split the dump file, we need to first switch split dump on with an allow_split: on option in the zmc_device_dumptypes file, then define the size of each part and add it to the device profile. So for each backup <device>.profile we add the option part_size and the corresponding file size for the parts. For example 20g for 20 Gigabytes or 1t for 1 Terabyte.

First enable splitting dump files:

In the file /etc/zmanda/zmc/zmc_aee/zmc_device_dumptypes

Find:
define dumptype zmc_device_attached_storage

Change:

allow_split: off

To:

allow_split: on

Second, define the split_size:

In the file /etc/amanda/<Backup_Name>/<Device_Name>.profile

Find:

tapetype:
auto_length: on
length: 3662m
length_display: m

After, add:

part_size: 100g

Note: The above example splits dumps into 100GB files (allowed options k/m/g/t)

The best general guideline is to set the part_size to 10% of the total tape size.

On average, Amanda may waste up to 50% of the part_size on each time. However, a large part_size will write fewer filemarks to tape, making for an easier manual restore using native tools (not using Amanda).

If you never foresee needing to restore manually for any reason then you could set the part_size very small. However if you wish to have the ability to fall back on, in emergency situations or when Amanda is simply not working, you should set this size slightly larger for an easier manual restore.

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