Barriers and journaling filesystems [LWN.net]

Barriers and journaling filesystems

Posted May 22, 2008 22:30 UTC (Thu) by brouhaha (subscriber, #1698)
In reply to: Barriers and journaling filesystems by ekj
Parent article: Barriers and journaling filesystems

i.e. it is impossible to wear out flash faster by writing repeatedly to the same location)

Actually that's not true. Many (possibly most) large flash memory cards have the wear leveling done in sections, so it's possible to wear out one section before the others.

The vendors tend to be fairly secretive about the details of their wear-leveling algorithms.

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Barriers and journaling filesystems

Posted May 23, 2008 2:29 UTC (Fri) by drag (subscriber, #31333) [Link]

What would be great would be to get flash manufacturers to, optionally, allow the OS to access
the flash media more directly as a MTD, which reflects the true nature of flash media.

This way Linux folks can take advantage of MTD-specific file systems that can handle wear
leveling in a very effective and open manner. (and probably get better performance, to boot)

(runnning MTD file systems on top of Block-to-MTD emulation in software on top of MTD-to-Block
emulation in hardware on top of MTD flash seems self-defeating..)

This way for the 'industrial' flash people using the flash for performance reasons on Unix
systems can get the most benefit while their Windows-using counterparts can continue to use
that stuff to speed up swap file access and application pre-caching in Vista using the block
emulation hardware.

wearing out Flash memory

Posted May 23, 2008 3:07 UTC (Fri) by sbishop (subscriber, #33061) [Link]

Part of the trouble is that people confuse Flash memory with devices implemented using Flash.
A location within a Flash memory chip, for example, will certainly wear out faster if it's
written to repeatedly.  The chips themselves do absolutely no wear leveling.  But, of course,
it would be insane to build a Flash-based device without built-in wear-leveling logic and CRC
checks, which may have been the reason for the "it is impossible to wear out flash faster by
writing repeatedly" comment.

By the way, I work for a memory manufacturer, and it's my job to do reliability testing on
this stuff.  My co-workers and I have all come to hate Flash.  It is expected that the chips
will wear out, and transient failures are okay.  The controllers are expected to deal with
these issues; it's the nature of the beast.  So what does "working" mean?!  Oh, and the state
machine of each one of these *#$%!@ things are different.  I miss DRAM...