Last Modified: Friday, 27-Mar-2009 14:06:50 EDT
CSB Filesystems -- Data Backup and Recovery
Summary
All non-temporary CSB filesystems are protected by multiple safeguards
against user error or system failure. Seven days' worth of snapshots of
all file systems are kept on line; permanent archives are made every 4-6
months. However, it is possible to defeat these efforts, and files can be
permanently lost. Users should understand the limitations of the measures
offered by the CSB, and take their own measures to protect essential data.
How CSB filesystems are protected
At present, /srv/frames is the only
filesystems designated for temporary storage.
Files on temporary storage are not protected in any way against mechanical or
human failure. All other filesystems are subject to the following safeguards.
RAID storage
All non-temporary CSB filesystems are stored on RAID hardware. This means
that if a single disk drive fails, no data are lost. The redundant data
are rebuilt onto a spare drive, and the defective drive is replaced.
Daily snapshots
Early every morning, a complete snapshot is taken of all non-temporary CSB
filesystems. The snapshot is stored on a server and RAID system completely
independent of the primary system. In the event of catastrophic failure of
the primary system, files can be recovered except for those modified since
the morning's backup.
Snapshots will be retained for 7 days (but see caveats below). If you
delete or modify a file, and later want to recover the original contents,
you can retrieve it from the online snapshot.
Archiving
Every 4-6 months, we create a "permanent" archive of all CSB non-temporary
filesystems. Before September 2006, these archives were made on magnetic
tape. Beginning with that date, we are using DVDs.
Tape Backup
Prior to September, 2006, a full backup of CSB filesystems was made
roughly every three months. Incremental backups were made roughly
every 10 days. The backups were made to tapes, which were re-used in
rotation. Recovery of lost files was time consuming, requiring searching
through various full and incremental backup tapes. This sytem has now been
discontinued.
Data Recovery
The staff will assist in any requests for data recovery. The 7-day daily
snapshot should allow for recovery of active files which are lost due to
error or system failure. Most files of enduring importance will be on the
filesystem long enough to be backed up on at lest oneof the 6-monthly
archives.
Caveats
-
If a filesystem is full or nearly full, and its contents are
substantially modified, some of its files may not be properly backed up
to the snapshot filesystems or the archives.
-
If a file is deleted before it has been on the system long enough to be
backed up in one of the semi-annual archives, then after seven
additional days have elapsed, the file will be permanently lost.
-
If a single file is larger than 4GB, it may not be archived.
-
Recovering archives depends on the availability of hardware capable of
reading the media on which the archive was written, and on age and
quality of the media itself. Magnetic tape, for example, has a half life
of about 5 years.We hope that DVDs will do better, and that DVD readers
will be available for some time to come.
-
We have tested these procedures, but with less rigor, we hope, than the
systems that protect data at the Social Security Administration or the
Department of Homeland Security. In any case we give no warranty,
express or implied.
Last Modified: Friday, 27-Mar-2009 14:06:50 EDT