Re: [9fans] Throwing in the Towel

[ori@eigenstate.org]

Finally,. SSDs just die over time. Especially if they are
not powered on and refreshing. JEDEC specs say that they
should retain data for 1 year unplugged when stored at 30
degrees celsius, assuming the internet isn't lying to me.

Keep backups.

Quoth Dave Eckhardt <davide+p9@cs.cmu.edu>:
> > For the napkin calculation: On disk, the IEntry is 38Bytes.  Alas,
> > writes occur always in (the ssd internal) blocksize.  So, essentially
> > (assuming 4096 byte blocksize, which is quite optimistic), we have
> > a write efficiency of less than 1 percent.
> 
> While I see how such a model can predict disaster, I don't think that
> model matches how FTLs work, because it can't.
> 
> Many file systems (FAT, ext2/3/4) write the same logical block over
> and over and over and over and over.  I think the default interval
> for ext4 to synch the superblock and the journal is five seconds,
> which if true is more than 15,000 times every *day* for a busy
> file system (and I think lots of Linux systems are busy in that
> sense).
> 
> > A good firmware in the ssd could avoid needing a new block for the
> > write, if all bits are changed in teh same direction by the new
> > data.
> 
> Again, I believe this model predicts that no regular Linux file
> system can be used on any SSD, thus I believe this model is not
> accurate.
> 
> To quote Wikipedia:
> 
>   https://en.wikipedia.org/wiki/Flash_memory_controller
> 
> > The mapping units of an FTL can differ so that LBAs are mapped
> > block-, page- or even sub-page-based.  Depending on the usage
> > pattern, a finer mapping granularity can significantly reduce
> > the flash wear out and maximize the endurance of a flash based
> > storage media.
> 
> Also, I feel as if this point is several assumption layers deep.
> I think one user reported an unknown number of failures in two
> sets of SSDs of unknown brand and model.  I don't think we know
> that it was venti SSDs that went bad as opposed to fossil SSDs,
> let alone knowing it was index SSDs for venti.
> 
> > It seems, venti in its current form is a ssd killer, if they
> > are used for the isects.
> 
> I don't think this claim is yet supported well.
> 
> Dave Eckhardt

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