[9fans] plan9ports venti with arenas on fat filesystem

[9fans] plan9ports venti with arenas on fat filesystem

[Adrian Tritschler]

I've been playing/experimenting with a p9p venti with arenas in 512M
files on linux ext3 file systems with no problems, today I decided to
set up a second venti on an external USB drive so I could have a backup
of it.  It seems that I can't create arenas on files on the USB fat32 disk.

% cd /mnt/venti
% venti/fmtarenas arenas6 ./arenas6
fmtarenas ./arenas6: 1 arenas, 536,076,288 bytes storage, 524,288 bytes
for index map
2007/1012 10:25:17 err 4: write ./arenas6 offset 0xc0000 count 49152 buf
8074000 returned 16384: Success
2007/1012 10:25:17 err 4: can't write arena set: write ./arenas6 offset
0xc0000 count 49152 buf 8074000 returned 16384: Success
can't write back arena partition header for ./arenas6: can't write arena
set: write ./arenas6 offset 0xc0000 count 49152 buf 8074000 returned
16384: Success

Copying the file to the ext3 system, performing the venti/fmtarenas then
copying it back works.

% rsync -P arenas[67] $HOME/tmp
arenas6
   536870912 100%    4.96MB/s    0:01:43 (xfer#1, to-check=1/2)
arenas7
   536870912 100%    4.61MB/s    0:01:51 (xfer#2, to-check=0/2)

sent 1073873034 bytes  received 64 bytes  5006401.39 bytes/sec
total size is 1073741824  speedup is 1.00

% cd $HOME/tmp
% venti/fmtarenas arenas6 ./arenas6
fmtarenas ./arenas6: 1 arenas, 536,076,288 bytes storage, 524,288 bytes
for index map
% venti/fmtarenas arenas7 ./arenas7
fmtarenas ./arenas7: 1 arenas, 536,076,288 bytes storage, 524,288 bytes
for index map

Then back on the USB fat32 system all *seems* to work:

% cd /mnt/venti
% rsync -P  $HOME/tmp/arenas6 .
 :
% venti/fmtindex venti.conf
fmtindex: 8 arenas, 23,800 index buckets, 4,288,479,232 bytes storage
% venti/venti -d -h tcp!localhost!1090 -a tcp!localhost!17036
2007/1012 10:40:42 venti: conf...httpd
tcp!localhost!1090...init...icache 0 bytes = 1,000 entries; 4 scache
sync...announce tcp!localhost!17036...serving.

As soon as venti/wrarena starts to write to it, many errors occur, all
seem to be of the form:

2007/1012 10:43:15 err 4: write ./isect1 offset 0x73c000 count 65536 buf
810c000 returned 16384: Success
venti/venti: part ./isect1 addr 0x10c000: icachewritesect writepart:
write ./isect1 offset 0x73c000 count 65536 buf 810c000 returned 16384:
Success

Is the correct answer, "just don't do that", am I doing something wrong,
or this a bug that anyone is interested in fixing?

	Adrian

Re: [9fans] plan9ports venti with arenas on fat filesystem

[Russ Cox]

The code is in /usr/local/plan9/src/cmd/venti/srv/part.c.
And it is very complicated.  Far too complicated, but hey,
that's modern Unix.

It looks like pwrite is being asked to write 64k and only
writing 16k.  That alone shouldn't be a problem unless
the code believes the fs block size is > 16k.

I don't see anything obviously wrong (it's that complicated)
but I would certainly accept bug fixes.  ;-)

Russ

Re: [9fans] plan9ports venti with arenas on fat filesystem

[Robert William Fuller]

Russ Cox wrote:
> The code is in /usr/local/plan9/src/cmd/venti/srv/part.c.
> And it is very complicated.  Far too complicated, but hey,
> that's modern Unix.
> 
> It looks like pwrite is being asked to write 64k and only
> writing 16k.  That alone shouldn't be a problem unless
> the code believes the fs block size is > 16k.

A FAT filesystem of that size should have a block size of 64K, no?