Re: Solaris ZFS on Linux [Was: Re: the " 'official' point of view" expressed by kernelnewbies.org regarding reiser4 inclusion]

David Masover
2006-08-01T01:31:37Z

Matthias Andree wrote:
> On Mon, 31 Jul 2006, Nate Diller wrote:
>
>> this is only a limitation for filesystems which do in-place data and
>> metadata updates. this is why i mentioned the similarities to log
>> file systems (see rosenblum and ousterhout, 1991). they observed an
>> order-of-magnitude increase in performance for such workloads on their
>> system.
>
> It's well known that transactions that would thrash on UFS or ext2fs may
> have quieter access patterns with shorter strokes can benefit from
> logging, data journaling, whatever else turns seeks into serial writes.
> And then, the other question with wandering logs (to avoid double
> writes) and such, you start wondering how much fragmentation you get as
> the price to pay for avoiding seeks and double writes at the same time.

So you use a repacker. Nice thing about a repacker is, everyone has
downtime. Better to plan to be a little sluggish when you'll have
1/10th or 1/50th of the users than be MUCH slower all the time.

You're right, though, to ask the question:

> TANSTAAFL, or how long the system can sustain such access patterns,
> particularly if it gets under memory pressure and must move.

Anyone care to run some very long benchmarks?

> Even with
> lazy allocation and other optimizations, I question the validity of
> 3000/s or faster transaction frequencies. Even the 500 on ext3 are
> suspect, particularly with 7200/min (s)ATA crap. This sounds pretty much
> like the drive doing its best to shuffle blocks around in its 8 MB cache
> and lazily writing back.

Oh, I'm curious -- do hard drives ever carry enough battery/capacitance
to cover their caches? It doesn't seem like it would be that
hard/expensive, and if it is done that way, then I think it's valid to
leave them on. You could just say that other filesystems aren't taking
as much advantage of newer drive features as Reiser :P

Anyway, remember that the primary tool of science is not logic. Logic
is the primary tool of philosophy. The primary tool of science is
observation.

Sorry, the only machines I could really run this on are about to be in
remote only mode for a couple weeks. I'm hesitant to hit them too hard.