Sizing Guide Exchange Server 2003 - Fujitsu

White Paper Sizing Guide Exchange Server 2003 Version: 4.2, July 2006
Backup
Backup is one of the most important components for
safeguarding data. With regard to high-availability hardware
resources there could be a tendency to neglect the backup of
mirrored data. Studies, however, show that only about 10% of
data loss is due to hardware and environmental influences. The
remaining 90% is split approximately into one half for data
losses as a result of software problems, such as program
errors, system crashes and viruses, and one half for data
losses as a result of reckless handling of the data by users and
administrators.
It is possible to eliminate part of the possible causes by means
of preventive measures. The hardware-induced causes for data losses can be intercepted by excellent
hardware equipment, as provided by Fujitsu. Fujitsu even offers a disaster-tolerant hardware platform for
Exchange servers for natural disasters. A good virus scanner should by all means be used with every
Exchange server in order to protect against data loss through viruses. Data loss as a result of reckless
handling can be reduced in an Exchange server by training the administrators accordingly. Nevertheless,
there is still great potential for possible data losses due to program errors, system crashes or human error. In
this case, prevention through reliable backup hardware or careful backup strategy is the only cure.
One action for avoiding data losses through program errors and system crashes is the transaction database
concept used by Exchange, which was already explained in the chapter Transaction principle. In it all
changes to the database are recorded in so-called log files. The log files, which are only written sequentially,
are for the most part immune to logical errors due to program errors, as can occur in a database with
complex data structures that is written and read on a permanently random basis. Furthermore, the data
volume of the log files is quite small compared with the database so that errors in the log files are statistically
speaking substantially less.
However, this transaction principle necessitates a regular backup, as otherwise the updating of all changes
to the database would in the long run take up a great deal of storage space. With an on-line Exchange
backup the log files are automatically deleted by Exchange
once the database backup has been completed. If the database
is lost, the database can - with the aid of a backup and the log
files that have been written since the last backup - be restored
with all the data of the time of the database loss. After a
database has been restored, Exchange automatically replays
the log files with all the changes since the backup.
Backup
+ =
Current
database
All versions of Exchange Server provide the option of carrying out a so-called on-line backup during ongoing
operations. In this way, the Exchange database can be backed up while all the services of Exchange - apart
from performance loss - are available without any restrictions. At the same time, it is of course possible to
carry out a so-called off-line backup. However, this is not an adequate method, as the Exchange services are
not available during the backup time, the data volume to be backed up is larger (because the database files
are backed up as a whole and not logically), no data check takes place and the log files are not purged
automatically. However, the essential disadvantage of an off-line backup lies in the fact that with a restore
the log files which have come into being since the compilation of the backup cannot be played back.
The choice of a suitable backup medium and suitable backup software has an altogether considerable
influence on the availability of the Exchange server. Whereas the backup can be carried out during the
ongoing operations of Exchange and the duration of a backup is thus not directly critical, the duration of a
restore is particularly decisive for availability. Since, in contrast to the backup, the Exchange services are not
unrestrictedly available during the restore. This is why when selecting a backup solution - hardware and
software - particular attention must be paid to speed in addition to reliability.
Exchange Server itself contains a number of features that accommodate a fast backup and restore. First with
Exchange 2000 Server, Exchange supports several databases and storage groups. Storage groups can be
backed up in parallel and databases can be restored individually. In the event of a restore only those users
are affected whose data are in the database to be restored. All other users can use the Exchange services
without any restrictions, apart from possible performance loss.
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