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- Newsgroups: comp.sys.amiga.applications
- Path: netnews.upenn.edu!dsinc!scala!news
- From: dave.haynie@scala.com (Dave Haynie)
- Subject: Re: "AFS" Ami-File Safe
- Sender: news@scala.scala.com (Usenet administrator)
- Message-ID: <1996Mar28.221141.9165@scala.scala.com>
- Date: Thu, 28 Mar 1996 22:11:41 GMT
- Distribution: na
- Reply-To: dave.haynie@scala.com (Dave Haynie)
- References: <150773@cup.portal.com> <4lCkP4eSMV1ZEHpSJ2@transarc.com> <4i41sb$kkd@ug1.plk.af.mil> <223e3aab.1d86ea54@ragnarok.mtroyal.ab.ca> <4isip4$8s9@ug1.plk.af.mil>
- Nntp-Posting-Host: gator
- Organization: Scala Computer Television, US Research Center
-
- In <4isip4$8s9@ug1.plk.af.mil>, rudd@ug1.plk.af.mil (Douglas Rudd) writes:
- >N94333765@ragnarok.mtroyal.ab.ca (blair wickstrand) writes:
-
- >>On Tue 96-Mar-12, Douglas Rudd said:
- >
- >> DR> AFS is nice enough if you don't need to recover a large number of
- >> DR> deleted files. DS4 can only work by salvage mode only, and is far
-
- >>Have you not heard of backups ?
-
- >Cute. Sometimes you just don't get that luxury. And it STILL is no
- >substitute for file recovery. Accidents happen. File recovery
- >is rather like seat belts and air bags. AFS doesn't give you
- >access to those.
-
- AFS will never be as robust for file recovery as FFS. One of the
- runtime advantages of AFS is its compact directory structure. You get
- fast directories because all of the file system overhead is localized,
- and also because more than one file can be cataloged per disk
- block. Under FFS, you have a disk block dedicated to each file or
- directory, in essence a distributed catalog structure. What makes FFS
- slower at directory scanning makes it great for file recovery.
-
- Even with deletes. When I delete an FFS entry, the pointer to that
- entry is removed from its directory's hash table, but the actual
- catalog information is intact until reallocated by the file
- system. Under AFS, the entry is physically detroyed. Along the way,
- AFS grew a small buffer of recently-deleted objects, which DiskSalv
- will eventually use. But even that is no great help if you accidently
- wack a directory with a hundred files in it. DiskSalv will look for
- older copies of the directory, which do tend to hang around until
- they're reallocated, but there's no guarantee the file is the same
- location any longer. This is further complicated by the fact that AFS
- catalogs things by handle, not direct reference. All references are
- made to "ANodes", which are handles that contain the physical
- references to things on-disk. This is especially annoying because you
- can't assume a 1:1 mapping between catalog contents and what's
- actually on disk, as you can with FFS.
-
- >> DR> from perfect with that -- it misses many subdirectories and renames
- >> DR> files with other file names. On a 1gb partition, I got about an
- >> DR> 80 percent recovery rate (usable) though there was no damage to the
- >> DR> drive -- just deleted files (about 200 mb worth).
-
- >>Which is better recovery rate than what I get from FFS when I did try
- >>it. Restoring from backups is much more reliable and much safer.
-
- It always depends on what you're doing, and what you've done since a
- deletion. Under FFS, you can delete every file and *DESTROY* every
- directory and still get back every file and the original directory
- structure. You can't get anything like this with AFS, though
- eventually I'll have a DS4 upgrade that uses a few new strategies to
- find more of what still may be there.
-
- >>Anytime you try salvaging a deleted file you risk the chance that part
- >>of that deleted file was overwritten by another.
-
- Sure. The key to Salvaging effectively is to run DiskSalv as soon as
- you know you need to run it. While it doesn't have to be this way, in
- every Amiga file system to date, deleted blocks may be immediately
- reallocated. They are, after all, deleted -- the computer doesn't know
- you were just kidding :-)
-
- >I get a fairly good rate of recovery from a disk which has not been
- >writen to after an accident under FFS. Not so under AFS. A simple
- >deletion of files with NO writes to that drive is beyond recovery
- >under AFS. It's that simple. The partition I refere to has not been
- >accessed since the deletion accept by DS4 for salvage only. No writes.
- >It is otherwise unmounted.
-
- That's really expected behavior at this point. It can get somewhat
- better, but no miracles are promised. DiskSalv can only find data
- based on some kind of clue still present on the disk. If every
- reference to a block of data has been eliminated from disk, there's no
- way to find that data, even if the data itself is still fully
- intact. That's a general rule, not something specific to AFS. It's
- just a rule more likely to assert itself on AFS versus FFS.
-
- Backups are still a good idea. AFS is far more typical of your
- situation on other systems, the robustness of FFS is fairly unusual.
-
- Dave Haynie | ex-Commodore Engineering | for DiskSalv 3 &
- Sr. Systems Engineer | Hardwired Media Company | "The Deathbed Vigil"
- Scala Inc., US R&D | Ki No Kawa Aikido | info@iam.com
-
- "Feeling ... Pretty ... Psyched" -R.E.M.
-
-