Weekend and Nightly Backups
There are three basic types of weekend and nightly backups:
1. Full backups – all
primary storage data is written to a set of tapes. If a full backup is performed
on 10TB of primary data, all 10TB will be written to a set of ten tapes every
weekend. Full backups are typically run for all data on all servers during the
weekend. In addition, certain applications like databases and email data stores
might also be backed up nightly as a full backup. Since the full backup process
consumes a tremendous amount of network bandwidth and client system processing
and storage cycles, full backups are typically performed on the weekend to
minimize the performance impact on users and applications.
2. Differential backups –
all primary storage data that has changed since the last full backup are written
to a set of tapes. If a full backup was completed on a Saturday night, a
Wednesday night differential backup would protect all of the files that were
created and changed on Sunday, Monday, Tuesday and Wednesday. If differential
backups were run every night, the size of backups and the time to perform
backups would become too great, so typically, differentials are run once or
twice in the middle of the week. The advantage of running a differential backup
is reduced time to restore files later in the week.
3. Incremental backups – all
primary storage data that has changed since the last incremental backup are
written to a set of tapes. With an incremental backup, since only changed files
are backed up, the time and burden on server and network resources is kept to a
minimum. The trade off of using a weekend full / daily incremental approach is
that if system or data loss occurs mid-week, the full backup has to be restored
first, and then each incremental backup has to be restored in successive order.
If a failure occurred on Thursday, first the data from the last full weekend
backup would be restored, followed by sequential restores from Monday, Tuesday
and Wednesday night’s incremental backups, which can significantly extend the
time it takes to restore data.
For each type of data in an organization, different backup
policies may be in effect. Here are some examples:
Email data store and database
backups may be performed as full backups daily to reduce the time it takes
to recover from a lost email data store or database. Performing a
restore from a series of full, incremental and/or differential tapes can
take much longer than just a restore from a recent full tape.
Most data is protected with
full backups on the weekend and incremental backups during the week. Some
organizations replace midweek incremental backups with midweek differential
backups to reduce the number of tapes that would be used during a restore
from later in the week.
Weekend and nightly backups are used to restore files that have
been accidentally deleted or have become corrupted. Most organizations maintain
between four weeks and 26 weeks of full backups and the last one to four weeks
of incremental / differential backup data on site. This allows users to request
the restoration of data from an earlier copy.
Historical data in the form of weekly and nightly backups may be
required by financial staff when third party auditors request financial
information as of a certain date. Lawyers, in response to legal inquiry or
subpoena may be required to produce these files from historical backup tapes.
Weekend and nightly backups typically require a duplicate tape
be created to keep a complete data set of all primary data off site in case of a
site disaster such as pipes bursting, natural flooding, hurricanes, tornadoes,
fires and other disasters.
A backup server is a standard server that has backup software
loaded onto it. Backup servers are connected to a local disk subsystem and/or
one or more tape drives within tape libraries. Backup servers also
communicate with servers, desktops and laptops to be backed up by having backup
client (agent) software loaded onto each system. The backup agent moves all data
with that server over the network to a backup server. Since the backup process
consumes client machine processing and storage cycles, backups are typically
performed at night to minimize the performance impact on users and applications.
Disk-based Storage for Weekend and Nightly Backups
Due to the complexity of managing tens to hundreds of tapes
created by weekend and nightly backups, and the challenges of quick and reliable
data restores from these tapes, most companies are moving to disk-based backup
at their primary site while maintaining tape for offsite data protection. This
combination provides faster, more reliable and more manageable local disk-based
backups and restores of data while keeping the cost of storing data offsite on
tapes at a minimum.