Tape backup performance on 386 ISA/EISA systems

Wm E. Davidsen Jr davidsen at sixhub.UUCP
Sun Jun 10 13:36:33 AEST 1990

In article <1990Jun8.223358.27138 at murphy.com> peterg at murphy.com (Peter Gutmann) writes:

| All of the tools required for disk de-fragmenting exist in the base
| distribution of UNIX. All it requires are three simple steps,
| 1) create a backup of the device using your favorite backup utility 
|    (such as tar or cpio). Don't use dump or any other utility which
|    creates a "image" of the file system.
| 2) erase the contents of the devices that has been backed up
|    in step one (above).
| 3) restore the device from the backup made above.
| what this accomplishes is that the device has all of the blocks
| in the file system moved to the free list. then reallocated sequentially
| from the backup.

  If you do step 2 via mkfs, or if you have a filesystems which uses a
bitmap, this is true. However, you said freelist, and in that case you
had better do an fsck with the -s option to order the freelist, or you
don't gain much.

  Since dump can be used between diferent size filesystems (given enough
room on the 2nd f/s) I believe that the information is logical rather
than physical, and that a restore defragments the disk. At least on this
(Xenix) system. A physical dump doesn't (dd /dev/rawdisk /dev/tape) type.
bill davidsen - davidsen at sixhub.uucp (uunet!crdgw1!sixhub!davidsen)
    sysop *IX BBS and Public Access UNIX
    moderator of comp.binaries.ibm.pc and 80386 mailing list
"Stupidity, like virtue, is its own reward" -me

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