CA-409710: Modify the default backup parameters

[BengangY]

The current default count of metadata backup files is 25. This number is too
many. For the customer in XSI-1873, the backup disk is 500 MB, and each backup
file is about 35 MB. So it can't keep 25 backup files.

A quick solution is to modify the backup parameters, including:

1. Reduce the default count of metadata backup files to 12.
2. Increase the backup VDI size to 1 GiB so it can keep more backup files.

[lindig]

The backup VDI is created by this script. So another solution is to create a larger VDI or to decide dynamically how many generations to keep.

[Vincent-lau]

Is it possible to make the backup disk larger? 500 MB seems to be quite small. Perhaps double the disk instead of half the back up file limit?

[lindig]

The number of generations kept is only the default and there is an option to override this. So what this change does is changing the default. But like I said above, we could also change the size of the VDI. The script already emits an alert when it is running low on space.

   vdi_uuid=$(${XE} vdi-create virtual-size=500MiB sr-uuid="${sr_uuid}" 

A change here obviously would only take effect when no VDI already exists.

[root@genus-34-35d ~]# xe-backup-metadata -h
Usage: /opt/xensource/bin/xe-backup-metadata [-h] [-i] [-u <SR UUID>]

 -h: Display this help message
 -c: Create a backup VDI if one cannot be found (default: false)
 -i: Initialize the backup VDI before performing the backup
 -u: UUID of the SR you wish to backup to
 -d: Dont perform a backup, but leave the disk mounted in a shell
 -k  Number of older backups to preserve (default: 25)
 -n: Just try to find a backup VDI and stop the script after that
 -f  Force backup even when less than 10% free capacity is left on the backup VDI
 -v: Verbose output


Use the -d option to examine the backup VDI, and restore it if necessary.
It is a good idea to copy the backup onto the control domain before
restoring it via the xe pool-database-restore CLI command.

[lindig]

Would have used "GiB" but GB works, too.

[Vincent-lau]

LGTM, as long as reducing the number of histories does not cause some violations of requirements