[9fans] wrarenas

[9fans] wrarenas

[Steve Simon]

Is wrarenas (write venti arenas back to disk) really really
slow or have I a hardware problem.

reading 10 arenas took 30secs or so, writing them into
a new venti (even with a bloom filter and DMA turned on)
took about 36 hours.

is this expected?

-Steve

Re: [9fans] wrarenas

[erik quanstrom]

On Fri Apr 24 13:51:18 EDT 2009, steve@quintile.net wrote:
> Is wrarenas (write venti arenas back to disk) really really
> slow or have I a hardware problem.
>
> reading 10 arenas took 30secs or so, writing them into
> a new venti (even with a bloom filter and DMA turned on)
> took about 36 hours.
>
> is this expected?

sidestepping the question about venti, a modern disk
with modern hardware should give >40mb/s; that is
	dd -if /dev/sdXX/data -of /dev/null -bs 512k -count 1000
should take < 12.5s.

- erik

Re: [9fans] wrarenas

[erik quanstrom]

and, writing should take the same amount of
time as reading.  that is you can switch -if and -of
and you should get the same results.

it could be that you are seeking around all over
the place.  on modern hardware, if you are doing
significant seeks between each write, you can get down
below 1mb/s.

i addressed this problem in the diskless fileserver paper.

- erik

Re: [9fans] wrarenas

[Russ Cox]

rdarenas reads directly from disk.
wrarenas writes to venti, which means
all of the network and seek overhead.
36 hours is too long, but it definitely
isn't going to run at disk speeds.
it sounds like your bloom filter wasn't
doing anything useful.

russ