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SubjectRe: soft update vs journaling?
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Jan Engelhardt wrote:
>>Unfortunately, journaling uses a chunk of space. Imagine a journal on a
>>USB flash stick of 128M; a typical ReiserFS journal is 32 megabytes!
>>Sure it could be done in 8 or 4 or so; or (in one of my file system
>>designs) a static 16KiB block could reference dynamicly allocated
>>journal space, allowing the system to sacrifice performance and shrink
>>the journal when more space is needed. Either way, slow media like
>>floppies will suffer, HARD; and flash devices will see a lot of
>>write/erase all over the journal area, causing wear on that spot.
> - Smallest reiserfs3 journal size is 513 blocks - some 2 megabytes,
> which would be ok with me for a 128meg drive.
> Most of the time you need vfat anyway for your flashstick to make
> useful use of it on Windows.
> - reiser4's journal is even smaller than reiser3's with a new fresh
> filesystem - same goes for jfs and xfs (below 1 megabyte IIRC)

Nice, but does not solve. . .

> - I would not use a journalling filesystem at all on media that degrades
> faster as harddisks (flash drives, CD-RWs/DVD-RWs/RAMs).
> There are specially-crafted filesystems for that, mostly jffs and udf.

Yes. They'll degrade very, very fast. This is where Soft Update would
have an advantage. Another issue here is we can't just slap a journal
onto vfat, for all those flash devices that we want to share with Windows.

> - You really need a hell of a power fluctuation to get a disk crippled.
> Just powering off (and potentially on after a few milliseconds) did
> (in my cases) just stop a disk write whereever it happened to be,
> and that seemed easily correctable.

Yeah, I never said you could cripple a disk with power problems. You
COULD destroy a NAND in a flash device by nuking the thing with
10000000000000 writes to the same area.

> Jan Engelhardt

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