Date: Fri, 18 Sep 1998 10:52:45 -0700 From: Robert Clark <Clark@open.org> To: "freebsd-questions@FreeBSD.ORG" <freebsd-questions@FreeBSD.ORG> Subject: Root Disk Backup. Message-ID: <36029DED.100E0A16@open.org>
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I'm trying to establish a set of tools that will minimize downtime when a root disk fails. Not because root disk failure is a frequent occurance, but when it happens, its always a key system at a bad time. Scenario: We have two dozen various UNIX systems, all important, all potential victims. (We generally keep everything except the OS and applications on a central NFS server.) My thought was: All systems should use the same brand and model of 2G SCSI HD. After the OS and apps are installed, take the HD out of the target system, install it into a FreeBSD system setup for this purpose, and dump a binary image of the HD to tape. Once a month, repeat the process, and dump a binary image of the HD to tape again. In the event of a root failure: Grab the most recent root-image tape for the system that failed. Grab a new 2G HD from the shelf. Pop the tape and HD into a FreeBSD system configured to restore the tape. Half an hour later, a replacement root disk is ready. (Or less time with a faster tape drive.) Why go to the trouble: It would seem difficult to fully backup a UNIX system while it is running. Taking the system offline would ensure that no changes are made to the disk while it is being backed up. Why use a FreeBSD system instead of the target platform? FreeBSD boots quickly, has a good variety of software available, and is supported by a great bunch of people. PC hardware can be small, light, and inexpensive. (Or cramped, flimsy, and cheap depending on your point of view.) Some types of UNIX can take hours to install from scrath. Shaving a few hours off the rebuild time would make people happy. This approach would seem to be platform independent. IE: I'm hoping to be able to backup Solaris and HP-UX without needing to master half a dozen different backup methods. To me, at some level, a root disk is just another piece of hardware. (Unless the OS is cagy about serial numbers.) Why should the OS care. Questions / assumptions: FreeBSD can backup a HD even if their is no FS FreeBSD recognizes? (I've worked with a few (non UNIX0 tools that need a (PC-style) partition table to do their jobs.) As long as the geometry of the replacement drive is the same, does this approach sound feasible? What commands / programs could I use under FreeBSD? Is anyone else out there doing anything like this? I realize I would be backing up unused space as well as data, but as long as it all fits on one tape, I'd be trading simplicity for time. In order to keep the amount of time a station is down during root-disk backups, I'm entertaining the idea of making the initial copy a disk to disk process. (And dump the second disk to tape a few minutes later.) I was hoping that disk to disk would be quite a bit faster than disk to tape. Compound Question: (More for info than for need.) Start with a clean HD. Creat a (UNIX) FS that uses the whole disk. Actively use the FS. When you delete (unlink?) a file on a UNIX FS, the data remains on the HD.(?) If you use the FS long enough won't most of the disk eventually contain deleted info? If you dump a binary image of said HD, compression won't do much. Even if the HD is only 10% in use, the compression algorithm won't know what is files, and what is deleted files. Since "undelete" isn't innate to UNIX, washing the disk at times of low utilization shouldn't hurt anything? (By washing I mean that deleted files be replace by a repeat pattern, ie all zeros. Is fschk any faster on a disk that has been washed? Dumping a binary image of a "washed" disk would seem to be faster. Washed areas should be easier to compress. Statement: If I'm totally offbase on this please let me know. Thanks for the time, [RC] To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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