Messages in this thread | | | Date | Mon, 31 Jul 2006 20:31:32 -0500 | From | David Masover <> | Subject | Re: Solaris ZFS on Linux [Was: Re: the " 'official' point of view" expressed by kernelnewbies.org regarding reiser4 inclusion] |
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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. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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