[Beowulf] SSD prices - q: how many writes/erases???
jakobi at acm.org
Fri Dec 12 07:35:26 PST 2008
On Fri, Dec 12, 2008 at 08:17:19AM -0600, Geoff Jacobs wrote:
> > Reliability is another question and I posted a quick response to
> > this list in a different email.
> This being my big concern with flash.
related is this topic on SSD / flashes:
what's the life time when changing the same file frequently?
aka "mapping block writes to cell erases"
aka "how many erases are possible?"
In the days of yore, that was the limitation on using flash, as
writing a block to the same physical location on the flash (for some
to be defined sense of physical location :)) requires a whole slew of
blocks (let's call it a 'cell', maybe containing a few dozens or
thousands of blocks?) to be erased and a subset of them to be written.
Does anyone have current and uptodate info or researched this issue
if so thanx!!
Some of the questions I see before checking recent kernel sources
- is there some remapping in the hardware of the ide emulation chip
space of say compactflash or usb sticks?
- is part of this possible in the ide-emulation in the kernel?
- or is part of this in the filesystem, that is suddenly after a
decade or more, the fs has to cope again with frequent bad blocks,
like the old bad blocks lists of the SCSI days 2 decades past?
[basically: is there some 'newish' balancing to limit / redistribute
the number of erases over all cells? Is there a way to relocate cells
that resist erasing, ...?]
- can I place a filesystem containing some files that are always
rewritten on flash and use say ordinary ext2 or vfat for this?
- might I even be able to SWAP on flash nowadays?
- Or do I still have to do voodoo with FUSE overlays or other tricks
to reduce the number of writes leading to cell erases? Maybe check if
there's a real log-structured filesystem available, that has seen
production use outside of labs (and doesn't fail by keeping its some
of its frequently changing metadata in always in the same location).
jakobi at acm.org
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