Re: file system for solid state disks

[James Courtier-Dutton]

Daniel J Blueman wrote:
> On 23 Aug, 07:00, Jan Engelhardt <jengelh@xxxxxxxxxxxxxxx> wrote:
>   
> > On Aug 23 2007 01:01, Richard Ballantyne wrote:
> >     
> > > What file system that is already in the linux kernel do people recommend
> > > I use for my laptop that now contains a solid state disk?
> > >       
> > If I had to choose, the list of options seems to be:
> >
> > - logfs
> >   [unmerged]
> >
> > - UBI layer with any fs you like
> >   [just a guess]
> >
> > - UDF in Spared Flavor (mkudffs --media-type=cdrw --utf8)
> >   [does not support ACLs/quotas]
> >     
>
> Isn't it that with modern rotational wear-levelling, re-writing hot
> blocks many times is not an issue, as they are internally moved around
> anyway? So, using a journalled filesystem such as ext3 is still good
> (robustness and maturity in mind). Due to lack of write buffering,
> perhaps a wandering log (journal) filesystem would be more suitable
> though? I use ext3 on my >35MB/s compact flash filesystem.
>
> I can see there being advantage in selecting a filesystem which is
> lower complexity due to no additional spatial optimisation complexity,
> but those advantages do buy other efficiency (eg the Orlov allocator
> reducing fragmentation, thus less overhead), right?
>
> Also, it would be natural to employ 'elevator=none', but perhaps there
> is a small advantage in holding a group of flash blocks 'ready' (like
> SDRAM pages being selected on-chip for lower bus access latency) -
> however this no longer holds when logical->physical remapping is
> performed, so perhaps it's better without an elevator.
>
> Clearly, benchmarks speak...but perhaps it would make sense to have
> libata disable the elevator for the (compact) flash block device?
>
> Daniel
>   

Also, sector read ahead will actually have a performance impact on 
Flash, instead of speed things up with a spinning disc.
For example, a request might read 128 sectors instead of the one 
requested at little or no extra performance impact for a spinning disc.
For flash, reading 128 sectors instead of the one requested will have a 
noticeable performance impact.
Spinning discs have high seek latency, low serial sector read latency 
and equal latency for read/write
Flash has low seek latency, high serial sector read latency and longer 
write than read times.

James

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