Re: Tuning for Compact Flash

[Christer Weinigel <christer@weinigel.se>]

Martin K. Petersen wrote:

>>>>>> "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.


Yeah, I wish some flash manufacturer would do the right thing and just 
stick some NAND chips and some PCI/PCIe glue on a CardBus/ExpressCard. 
Something that allows a Linux driver to talk directly to the flash chips 
and then a simple DMA engine to do bus mastering block transfers to and 
from memory.  We could then run yaffs or whatever we wanted on it with 
no translation layers at all in between.

> 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.

That sounds just horrid.  Oh well, I won't have much choice when my hard 
drive dies, drives in this form factor are not manufactured any more and 
the only thing that will fit into the slot is a Compact Flash card or 
maybe with some hacking a USB drive.  :-)

  /Christer