From: Pat LaVarre <p.lavarre@ieee.org>
To: David Woodhouse <dwmw2@infradead.org>
Cc: "Phillip Lougher" <phillip@lougher.demon.co.uk>,
"Matthew Wilcox" <willy@debian.org>,
"Erez Zadok" <ezk@cs.sunysb.edu>,
"Jörn Engel" <joern@wohnheim.fh-wedel.de>,
"Kallol Biswas" <kbiswas@neoscale.com>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: partially encrypted filesystem
Date: 09 Dec 2003 16:40:54 -0700 [thread overview]
Message-ID: <1071013254.24032.13.camel@patibmrh9> (raw)
In-Reply-To: <1070883425.31993.80.camel@hades.cambridge.redhat.com>
> Even if you were going to admit to having a block size of 64KiB to the
> layers above you,
Within pdt x05 dvd/ cd, as contrasted with pdt x00 hdd/ flash, since
1999 we have an ansi t10 paper standard for a device to report bytes per
write block inequal to bytes per read block i.e. the 1999 mmc x0020
RandomWritable "feature" that describes a disc in a drive.
I haven't yet seen an fs run in Linux that bothers to fetch this plug 'n
play data, hence my op x46 GPCMD_GET_CONFIGURATION patches of
linux-scsi.
> you just can't _do_ atomic replacement of blocks,
> which is required for normal file systems to operate correctly.
Google tells me cd-rw and dvd+rw likewise do not support random writing
without load balancing e.g.
http://fy.chalmers.se/~appro/linux/DVD+RW/
http://fy.chalmers.se/~appro/linux/DVD+RW/#udf
"... As you might know DVD+RW media can sustain only around 1000
overwrites. The thing about fully fledged file systems is that every
read [or tight bunch of 'em] is accompanied by corresponding i-node
update or in other words a write! ..."
> These characteristics of flash have often been dealt with by
> implementing a 'translation layer' -- a kind of pseudo-filesystem --
> which pretends to be a block device with the normal 512-byte
> atomic-overwrite behaviour. You then use a traditional file system on
> top of that emulated block device.
Ick.
Naive read-modify-write to raise bytes-per-write-block passed-thru drops
thruput like 7X in the benchmarks I've seen.
Pat LaVarre
next prev parent reply other threads:[~2003-12-09 23:41 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-12-03 21:07 partially encrypted filesystem Kallol Biswas
2003-12-03 21:44 ` Richard B. Johnson
2003-12-03 23:20 ` bill davidsen
2003-12-03 21:44 ` Jörn Engel
2003-12-04 0:08 ` Linus Torvalds
2003-12-04 1:25 ` Jeff Garzik
2003-12-04 2:08 ` Linus Torvalds
2003-12-04 3:59 ` H. Peter Anvin
2003-12-04 2:37 ` Charles Manning
2003-12-04 14:17 ` Jörn Engel
2003-12-04 15:20 ` Linus Torvalds
2003-12-04 16:07 ` Phillip Lougher
2003-12-04 17:26 ` Jörn Engel
2003-12-04 18:20 ` Phillip Lougher
2003-12-04 18:40 ` Jörn Engel
2003-12-04 19:41 ` Erez Zadok
2003-12-05 11:20 ` Jörn Engel
2003-12-05 16:16 ` Erez Zadok
2003-12-05 19:14 ` Matthew Wilcox
2003-12-05 19:47 ` Erez Zadok
2003-12-05 20:28 ` Matthew Wilcox
2003-12-05 21:38 ` Pat LaVarre
2003-12-06 0:15 ` Maciej Zenczykowski
2003-12-06 1:35 ` Pat LaVarre
2003-12-06 2:39 ` Valdis.Kletnieks
2003-12-06 11:43 ` Maciej Zenczykowski
2003-12-07 0:04 ` Shaya Potter
2003-12-08 14:08 ` Jörn Engel
2003-12-06 0:50 ` Phillip Lougher
2003-12-08 11:37 ` David Woodhouse
2003-12-08 13:44 ` phillip
2003-12-08 14:07 ` David Woodhouse
2003-12-10 1:16 ` [OT?]Re: " Charles Manning
2003-12-10 17:45 ` Phillip Lougher
2003-12-09 23:40 ` Pat LaVarre [this message]
2003-12-10 0:07 ` Pavel Machek
2003-12-10 1:28 ` Pat LaVarre
2003-12-10 2:13 ` Charles Manning
2003-12-05 19:58 ` Pat LaVarre
2003-12-08 11:28 ` David Woodhouse
2003-12-08 13:49 ` phillip
2003-12-04 19:18 ` David Wagner
2003-12-05 13:02 ` Jörn Engel
2003-12-05 17:28 ` Frank v Waveren
2003-12-05 23:59 ` David Wagner
2003-12-19 15:01 ` Rik van Riel
2003-12-04 3:10 ` Valdis.Kletnieks
2003-12-04 18:16 ` Hans Reiser
2003-12-06 19:56 Pat LaVarre
2003-12-06 22:07 ` Maciej Zenczykowski
2003-12-10 3:22 Valient Gough
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