Tim wrote:
> Having said all that, I much prefer how another OS I used to work,
> worked. Writes to drives were completely completed (file written to the
> disc, plus the directory data updated) in one go, and you could pull a
> disc out moments later. There was no mounting or unmounting. And
> drives like USB memory sticks would be well served if they could work
> that way, since people do pull them out without going through a dismount
> process.
AmigaDOS?
Unfortunately, the nature of flash memory makes this a poor trade-off.
On something like the Amiga, floppy writes were slow enough (and floppy
space limited enough) that programs tended not to continually write data
to disk unless it was fairly necessary. That meant that it was very
reasonable to write all changes to disk immediately.
On modern operating systems, programs expect the hard disk to be
relatively fast and writes to be buffered by the operating systems. Some
approaches to disk (especially mmap, which merges the idea of “writing
to memory” and “writing to disk”) positively encourage programs to keep
changing the contents of files. But flash memory has a limited number of
write cycles: if you keep overwriting the same data constantly, you’ll
be using up those write cycles, hastening the day when the stick goes
read-only.
man mount says:
sync All I/O to the filesystem should be done synchronously.
In case of media with limited number of write cycles
(e.g. some flash drives) “sync” may cause life-cycle
shortening.
and notes:
the sync option today has effect only for ext2, ext3, fat, vfat and
ufs)
Weirdly, that implies ext4 doesn’t support sync. It does support
commit=1, which looks like it’s nearly identical.
Hope this helps,
James.
--
E-mail: james@ | “The letters are Elvish, of an ancient mode, but the
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