Configuring file-backed Venti stores
D1274749868
Aleimy
#Since I needed this, I figured it might be useful for others. Venti
#can be used with files on your Fossil as backing storage. There is
#no steadfast need to create partitions for Venti to run (and in some
#cases, this configuration may even be more convenient, for example
#when you're on a laptop with frequently added and erased data). I
#was bitten by a couple of problems that I figured out after reading
#the manpages several times, so I'll list them here so that you don't
#have to.
#
#My first step was to create the index file. I have no idea how large
#this needs to be, mathematically, compared to the size of the Venti
#arena. I suppose it would be something like:
#
#(arena_size / arena_block_size) / x
#
#Where x is however large a Venti index datastructure is. I could
#find this if I read the paper or source, but I'm too lazy right now.
#
#To create these files, I simply ran:
#
#! % dd -if /dev/zero -of isect0 -bs 8192 -count 10000
#! % dd -if /dev/zero -of arenas0 -bs 8192 -count 40000
#
#When these completed, the following files were present:
#
#! --rw-rw-r-- M 8 dho dho 327680000 Apr 3 20:10 arenas0
#! --rw-rw-r-- M 8 dho dho 81920000 Apr 3 20:10 isect0
#
#After this, I simply created a venti.conf file that was the same as
#the one in the manpage:
#
#! % cat > venti.conf
#! index main
#! isect /usr/dho/isect0
#! arenas /usr/dho/arenas0
#!
#! %
#
#Then I had the task of formatting these files. First I ran:
#
#! % venti/fmtisect isect0 isect0
#
#This took a little while. In retrospect, I could have used -Z, since
#I created this file with /dev/zero. The -Z flag tells fmtisect and
#fmtarenas to not zero the ``partition'' first, which is superfluous
#since we created the files from zero.
#
#After this, I ran:
#
#! % venti/fmtarenas arenas0 arenas0
#
#I should have used -Z here as well. Hereafter,
#
#! % venti/fmtindex venti.conf
#
#Yay, all's well, right?
#
#! % venti/venti -c /usr/dho/venti.conf
#! % venti=127.0.0.1
#! % vac -f test.vac testfile
#
#Instead of getting anything useful, I got some error about how I had
#no space in my arena. This didn't make much sense until I read the
#fmtarenas section of the manpage a few more times: Venti creates its
#arenas with a default size of 500MB. Mine's smaller, and since it
#didn't fulfill the size requirement, I didn't get _any_ Venti
#storage. Lame.
#
#So, I went back through and ran:
#
#! % venti/fmtisect isect0 isect0
#! % venti/fmtarenas -a 327680000 arenas0 arenas0
#! % venti/fmtindex venti.conf
#
#I didn't use -Z here, since the fmtindex actually writes to the
#index file. (And I wasn't sure if it wrote to the arenas file too).
#The -a flag specifies a size other than 512MB to use for the arena.
#Apparently this value should always be set to the size of the arena
#file or partition. (Fancy that!)
#
#After this:
#
#! % vac -f test.vac test
#! packet: 1/9 frag: 1/6 small mem: 1/1 big mem: 1/8
#! % ls -l
#! d-rwxrwxr-x M 8 dho dho 0 Apr 3 19:15 test
#! --rw-rw-r-- M 8 dho dho 45 Apr 3 20:10 test.vac
#! % cat test.vac
#! vac:d3d2b67810fb0fc289073c4b0c3ac6d9b01010fb
#
#Hope that's useful to someone.
#
#--dho
#
#Does this procedure basically work on Plan 9 Port for Unix-like
#systems as well? (Dave Leimbach)
#
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