8.15. Ease of Recovery I often quote an old coworker of mine, "No one cares if you can back uponly if you can restore."[#] Ease of recovery and speed of recovery often are overlooked when evaluating backup products. Many small factors can make doing restores either very easy or impossible: [#] Ron Rodriguez gets credit for this one. Replacing Ron as "backup boy" was my first job in this field. I have no idea how many times Ron said this, but I guess it sunk in. Platform independence -
This is a very important factor. Some products have gone to the trouble to ensure that every volume made by every version of their software can be read by every other version, no matter what platform it was made on. If this has been done, and a client is destroyed, its data still can be recovered, even if the replacement version is not of the same type. If volumes are not platform-independent, an administrator might need to keep a functional machine of each operating system version just for restores.[**] Having true platform independence also makes doing regular restores much easier. [**] Believe me, I know! I know of one place that still keeps around one or two AT&T 3b2s running SVr3 because of all the old cpio backups made on QIC drives that are unreadable on other platforms. Parallel restore -
This can be a very nice feature. When restoring a large directory or filesystem, the backups for that filesystem may be spread out over several volumes. Some products are able to read all these volumes at once, actually making the restore faster than the backup. When investigating this possibility, you also should find out if these volumes can be loaded in any order. User restores -
Some environments have sophisticated users who like to be able to do their own restores. If this is true in your environment, this feature will come in handy. Those who do not want users doing their own restores will want to know whether this feature can be disabled. Relocated restores -
This is very important. You sometimes need to restore a file that was originally located on another system. This different location may be a different host or a different directory. Some products do not allow this. Bare-metal restores -
A bare-metal restore is restoring a system from scratch, without even having a functioning operating system. (See Part V of this book for more information about bare-metal recoveries.) This is sort of the Holy Grail of backupsthe ability to restore an entire system from nothing. Several products now offer bare-metal recovery for one or more platforms. Multiple versions -
This is also very important. A lot of backup products not only track the most recent version of a file that was backed up but also track all versions of the file that are on backup volumes. Sometimes it's necessary to restore a file to the way it looked four days ago. Tracking deleted files -
This one surprises many people. Suppose there is a filesystem that changes quite a bit. New files are added and deleted every day. (A good example of this would be where Oracle's archived redo logs go. Hundreds of files may be added and deleted every day.) When asking the backup software to restore this filesystem, you might expect it to restore the filesystem the way it looked yesterday. Unfortunately, many products will instead restore allfiles that were ever located in that directory! It takes extra effort on the part of the software to "notice" that a file has been deleted and to not restore it unless told to do so. Failure to track deleted files can make restoring some filesystems very difficult. Overwriting options -
Has a user ever called and said that he blew away half his home directory because he typed rm -r * by accident? This user doesn't want the program to blow away everything in his directory by restoring on top of it. A good way to protect against that is to tell the backup software to "restore everything in here, except those files that are newer than what we have on backup." There are a number of other overwriting options, such as unconditional overwrite, prompt before overwrite, and don't overwrite the same exact file. |