Re: Tuning for Compact Flash

["Martin K. Petersen" <martin.petersen@oracle.com>]

>>>>> "Christer" == Christer Weinigel <christer@weinigel.se> writes:

Christer> Of course it won't behave like a hard drive, but it would be
Christer> nice if there was a file system with performance that didn't
Christer> suck as badly on a compact flash.

Well, you are limited by the capabilities of the FTL.  And as far as
CF goes the FTL is usually pretty braindead.

Making sure things are properly aligned really helps on "real" SSDs as
well as 4KB hw sector drives.  I'm working on some code that exposes
these parameters so we can perform that alignment when creating
filesystems.

But as far as CF is concerned I have tested many and not found a
single one that is suitable for a regular (random) filesystem write
workload.  To the extent that for embedded devices I ended up putting
a root filesystem tarball on the CF and unpacking it into ramfs during
boot.

And just to give you an idea: I'm getting two orders of magnitude less
random write ops on a (high-performance) CF than on a flash SSD from
the same vendor.  In both cases with I/O aligned to the flash page
boundary.

-- 
Martin K. Petersen	Oracle Linux Engineering