On Tue, Oct 19, 2004 at 12:59:42AM +0200, Wesley W. Terpstra wrote: > To which, I say, wtf!
You're using it wrong. > ... and yet par2 tells me I need 1909 more (I have 101). > That means I would need 18* more information in order to recover foo.pdf! > I have to admit, I am surprised by this. I would have expected a better > ratio, even with very old techniques. First off, I'm going to use PAR, since it's much simpler and in many cases a better choice than par2. (Par2 allows recovering files which have internal corruption, which is useful for completing almost-complete Bittorrented files.) You need to split files separately for PAR to work as you want. This is done just about everywhere on Usenet binary groups these days. I'm going to use split(1); people on Usenet, unfortunately, have a habit of using RAR. Let's create a 16-meg file: 07:27pm [EMAIL PROTECTED]/11 [~/z] dd if=/dev/urandom of=testing bs=1048576 count=16 16+0 records in 16+0 records out Split it into parts, not necessarily of even size: 07:29pm [EMAIL PROTECTED]/11 [~/z] split -b 1000000 testing testing.part. 07:29pm [EMAIL PROTECTED]/11 [~/z] ls -l total 32824 -rw-r--r-- 1 glenn users 16777216 Oct 18 19:28 testing -rw-r--r-- 1 glenn users 1000000 Oct 18 19:29 testing.part.aa -rw-r--r-- 1 glenn users 1000000 Oct 18 19:29 testing.part.ab -rw-r--r-- 1 glenn users 1000000 Oct 18 19:29 testing.part.ac -rw-r--r-- 1 glenn users 1000000 Oct 18 19:29 testing.part.ad -rw-r--r-- 1 glenn users 1000000 Oct 18 19:29 testing.part.ae -rw-r--r-- 1 glenn users 1000000 Oct 18 19:29 testing.part.af -rw-r--r-- 1 glenn users 1000000 Oct 18 19:29 testing.part.ag -rw-r--r-- 1 glenn users 1000000 Oct 18 19:29 testing.part.ah -rw-r--r-- 1 glenn users 1000000 Oct 18 19:29 testing.part.ai -rw-r--r-- 1 glenn users 1000000 Oct 18 19:29 testing.part.aj -rw-r--r-- 1 glenn users 1000000 Oct 18 19:29 testing.part.ak -rw-r--r-- 1 glenn users 1000000 Oct 18 19:29 testing.part.al -rw-r--r-- 1 glenn users 1000000 Oct 18 19:29 testing.part.am -rw-r--r-- 1 glenn users 1000000 Oct 18 19:29 testing.part.an -rw-r--r-- 1 glenn users 1000000 Oct 18 19:29 testing.part.ao -rw-r--r-- 1 glenn users 1000000 Oct 18 19:29 testing.part.ap -rw-r--r-- 1 glenn users 777216 Oct 18 19:29 testing.part.aq and then: 07:31pm [EMAIL PROTECTED]/11 [~/z] parchive a -n 5 testing.par testing.part.* ... 07:32pm [EMAIL PROTECTED]/11 [~/z] ls -l testing.p?? -rw-r--r-- 1 glenn users 1001558 Oct 18 19:32 testing.p01 -rw-r--r-- 1 glenn users 1001558 Oct 18 19:32 testing.p02 -rw-r--r-- 1 glenn users 1001558 Oct 18 19:32 testing.p03 -rw-r--r-- 1 glenn users 1001558 Oct 18 19:32 testing.p04 -rw-r--r-- 1 glenn users 1001558 Oct 18 19:32 testing.p05 -rw-r--r-- 1 glenn users 1558 Oct 18 19:32 testing.par Now all I need is enough parts: 07:32pm [EMAIL PROTECTED]/11 [~/z] mkdir partial 07:32pm [EMAIL PROTECTED]/11 [~/z] cp testing.part.* partial/ 07:33pm [EMAIL PROTECTED]/11 [~/z] rm partial/testing.part.ah 07:33pm [EMAIL PROTECTED]/11 [~/z] du partial 16444 partial 07:33pm [EMAIL PROTECTED]/11 [~/z] cp testing.p02 partial/ and recover: 07:33pm [EMAIL PROTECTED]/11 [~/z/partial] parchive r testing.p02 Checking testing.p02 testing.part.aa - OK testing.part.ab - OK testing.part.ac - OK testing.part.ad - OK testing.part.ae - OK testing.part.af - OK testing.part.ag - OK testing.part.ah - NOT FOUND testing.part.ai - OK testing.part.aj - OK testing.part.ak - OK testing.part.al - OK testing.part.am - OK testing.part.an - OK testing.part.ao - OK testing.part.ap - OK testing.part.aq - OK Restoring: 0%....10%....20%....30%....40%....50%....60%....70%....80%....90%....100% testing.part.ah - RECOVERED and join: 07:33pm [EMAIL PROTECTED]/11 [~/z/partial] cat testing.part.* > testing 07:34pm [EMAIL PROTECTED]/11 [~/z/partial] diff testing ../testing 07:34pm [EMAIL PROTECTED]/11 [~/z/partial] Alternatively, I can work exclusively with PAR files (though there's rarely any reason to do this), by creating enough PARs so their sum is large enough to recreate the file: 07:35pm [EMAIL PROTECTED]/11 [~/z] parchive a -n 20 testing.par testing.part.* 07:35pm [EMAIL PROTECTED]/11 [~/z] mkdir testing2 07:36pm [EMAIL PROTECTED]/11 [~/z] cp testing.p?? testing2 07:36pm [EMAIL PROTECTED]/11 [~/z/testing2] parchive r testing.p13 07:36pm [EMAIL PROTECTED]/11 [~/z/testing2] cat testing.part.* > testing 07:37pm [EMAIL PROTECTED]/11 [~/z/testing2] diff testing ../testing 07:37pm [EMAIL PROTECTED]/11 [~/z/testing2] This is exactly what you describe. -- Glenn Maynard
