Added documentation about backup_file_size about memory usage

I just spent a while chasing phantom OOM crashes in the backup
agent; I'm hoping this comment will help future users avoid
my problem.

Change-Id: I58ff10d212283b032cabf623021d3955111ff8f0
changes/18/820918/2
Andrew Bogott 1 year ago
parent 6d4a6aa978
commit b661d115f5

@ -41,7 +41,10 @@ posixbackup_service_opts = [
default=BACKUP_FILE_SIZE,
help='The maximum size in bytes of the files used to hold '
'backups. If the volume being backed up exceeds this '
'size, then it will be backed up into multiple files.'
'size, then it will be backed up into multiple files. '
'backup_file_size also determines the buffer size '
'used to build backup files, so should be scaled '
'according to available RAM and number of workers. '
'backup_file_size must be a multiple of '
'backup_sha_block_size_bytes.'),
cfg.IntOpt('backup_sha_block_size_bytes',

@ -141,7 +141,9 @@ deduplication or compression on the backup data.
The option ``backup_file_size`` must be a multiple of
``backup_sha_block_size_bytes``. It is effectively the maximum file size to be
used, given your environment, to hold backup data. Volumes larger than this
will be stored in multiple files in the backup repository. The
will be stored in multiple files in the backup repository. ``backup_file_size``
also determines the buffer size used to produce backup files; on smaller hosts
it may need to be scaled down to avoid OOM issues. The
``backup_sha_block_size_bytes`` option determines the size of blocks from the
cinder volume being backed up on which digital signatures are calculated in
order to enable incremental backup capability.

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