Why Tape Storage is Still Necessary
All this talk of the cloud, virtualization, and solid state storage, makes talking about tape backup systems seem rather boring. Still, tape backup systems are either an important part of IT operations or totally not necessary depending on the application. Tape storage, is a data storage device that reads and writes data on a magnetic tape. Tape costs less that SAN, SCSI internal, or PCI storage and is necessary for recovery in some instances. It is needed to meet long-term storage requirements mandated by business and legal needs and for compliance with government regulations. The falling price of disk storage makes tape backups less attractive especially as you factor in the administrative costs of maintaining the tape-backup system. Not all situations are suitable for a tape-backup strategy.
First of all, let’s say this: You cannot backup heavily-used databases that are continually changing. This is a radical idea, but if you look at the details it makes perfect sense. No matter what the vendors say, such backups are practically worthless. Why is this? Let’s look at the details.
Consider an LDAP system used to authenticate users to a web site. LDAP servers typically replicate their data from one server to another for performance and redundancy (i.e. backup). Users create dozens or maybe thousands of accounts per day. If there are, say, three servers and one of them is corrupt, you can recover that server from either of the remaining two. There is no downtime, because the system can run on two servers. In the case of a complete outage of all three servers–an event that is not very likely–you would have to restore from tape. Were you to do that, you would lose at least one day of business transactions plus down time. LDAP backups are usually made by exporting the LDAP format to plain text and then backing that up once per day. You should not back it up in its native format, because you cannot restore it in its native format as easily as you can from a text file. You probably could restore the data from tape, then roll forward to the current time, since the change log is not backed up any more than once per day.
Having read that, do you still believe it is worth backing up a database to tape?
Tape backup makes sense when an individual file is all that you need. That would include individual documents or files on a UNIX server–if one is lost, it can be recovered from tape. Active Directory is a kind of LDAP server, so a failover disk architecture is the backup strategy for that. Source code obviously can be backed up as you can backup the source-code-versioning system. Email must be backed up for legal reasons, since emails from executives are frequently targets of subpoenas.
What other systems are good candidates for tape backup? In the USA, SOX (Sarbanes-Oxley) requirements stipulate that certain data must be kept for a certain period of time–most international corporations sell stock on the American stock exchanges, so they are subject to American SOX requirements as well.
Consider a network and application-auditing and monitoring system. That system, because it is attached to firewalls, routers, Active Directory, and more, can contain millions of records per day. The system grows slower as it grows larger. These types of systems usually have an ability to archive the data into an off-line partition. You can restore these offline partitions when necessary, but if it is offline, you could back it up to tape, then put the tape into storage.
Another example is an accounting system. Some accounting systems at the end of the fiscal year allow you to bundle individual debits and credits into one file and then move that data offline. That too is a good candidate for tape backup. It does not make much sense to keep 15 years of financial transactions online.
In addition to replicating data to a failover system, one can use disk storage as a backup platform instead of tape. Data could be moved from high-cost fiber-channel SAN or flash-devices onto low-cost SCSI devices. The data is retained there for some time, and, if space becomes an issue, it can be moved onto tape; that is a hybrid backup strategy sometimes called “disk-to-disk-to-tape (D2D2T).
In sum, tape can be useful but is not appropriate in all circumstances. While many people will disagree, using tape to backup a rapidly-changing database is probably not worth the effort and expense, since for all practical purposes it cannot be used for recovery.
