ballen@convex.csd.uwm.edu (Bruce Allen) (05/10/91)
I am thinking about buying a high-capacity tape drive. There seem to be two options: 8mm exabyte for $1800 or 4mm hp DAT for $1500. The first has about 1.5 Gig capacity (I am told) and the second about 1 Gig. Two questions: 1. Is one of these two tape devices better, faster, more reliable? 2. Is there any good window based software that I can use, not only for backing up partitions but also for backing up useful directories that I don't want to keep around. This would let you search through directory trees easily, etc. Something a bit nicer than restore -i.
bet@zachary.mc.duke.edu (Bennett Todd -- gaj) (06/28/91)
I prefer Exabytes. They are available in two formats. The Exabyte model 8200 drive writes 2.4G on a tape; the model 8500 writes 5G on a tape. Any day now they are supposed to fix a firmware bug in the 8500, after which it will be able to read tapes written on an 8200. The fix will be made available as a field upgrade to the firmware. I have two reasons for preferring Exabytes. First, the capacity is somewhat higher even for the older 8200 format. Second, the media is widely available, and rather cheaper (I am getting Sony P6-120MP for $5.39ea, Fuji P6-120MP for $4.89ea, and TDK DAT for $12.00ea, all from the best source I've been able to find, quantity 100). Third (Three Reasons -- I have *Three* reasons) it got itself established rather sooner as a viable standard, so I can send Exabytes to other installations with far more confidence that they will be able to read them, than I have with DATs. I buy all my Exabyte drives from Delta Microsystems. They provide device drivers for all varieties of Suns under all releases of SunOS. The Delta Microsystems device driver is needed to make the things work under older releases of SunOS, and it makes more of the drive's capabilities accessible to software even under newer SunOS releases. They also sell windows-based software for organizing backups of your network, that can keep on-line indices and generally makes the backup and restore procedures user-friendly. I haven't as yet tried using their software; I've had good success with a system of shell scripts and a perl program. I am currently backing up about 17G of disk onto two 8200 drives. I maintain a master database, one record per filesystem, describing what machine the filesystem is on, the name of the filesystem, its size, and the command to use to back it up. On those machines that have dump/restore I use those; our Iris (which doesn't come with dump/restore) uses a simple shell script for taking multi-level dumps using find, cpio, and a set of timestamp files (one for each filesystem for each dump level). I run a perl program that reads this master database and writes out databases describing each tape; a full is currently taking 8 tapes, which I run one per night. On the other drive I run, each night, an incremental tape covering all those filesystems not getting a full that night. I've arranged for the perl program to set the dump levels in the backups to implement what the old BSD dump(8) man page described as ``Modified Tower of Hanoi'' rotation. This schedule, which goes (3, 2, 5, 4, 7, 6, 9, 8) has the characteristic that each tape backs up the changes only for the last two days, which preserves some redundancy (any file should make it onto two backup tapes) while keeping a ceiling on the amount of time an incremental is attempting to cover. I haven't yet stretched this approach to its limits; I am sure it will keep working past 20G, and I have hopes I can mung it into working out to 50G or more -- not bad for using two 2.4G tapes per night, and backing up everything every night. How far you can stretch it will of course depend on how quickly your users generate new data. I believe this kind of strategy scales about as well as can be hoped for -- which isn't in the least surprising, since the basic technology was developed for backing up several gig on old 9-track reels. -Bennett bet@orion.mc.duke.edu