choice of flash file system for large read-only volume

choice of flash file system for large read-only volume

[Hamish Moffatt]

Hi,
I hope end-user questions are ok here. Don't want to distract from
choosing new file systems names etc ;)

On a system I'm developing I'll have a root file system on NAND
flash, which will be read-only in normal use. This file system might be
in the order of 128Mb or 256Mb. (We want to be able to write to it in 
the lab during development, but in production we'll erase/rewrite the 
whole volume).

What would be a good choice of file system for this application? Does it
come down to JFFS2 versus YAFFS, or are there other alternatives?

I understand that JFFS2 mount times are proportional to the size; mount
time isn't critical to me but I would like the system to boot as quickly
as possible. Is YAFFS better in this regard?


thanks,

Hamish
-- 
Hamish Moffatt VK3SB <hamish@debian.org> <hamish@cloud.net.au>

Re: choice of flash file system for large read-only volume

[Jörn Engel]

On Thu, 17 May 2007 00:22:38 +1000, Hamish Moffatt wrote:
> 
> I hope end-user questions are ok here. Don't want to distract from
> choosing new file systems names etc ;)

Hehe.  Better keep your head down when such discussions start. :)

> On a system I'm developing I'll have a root file system on NAND
> flash, which will be read-only in normal use. This file system might be
> in the order of 128Mb or 256Mb. (We want to be able to write to it in 
> the lab during development, but in production we'll erase/rewrite the 
> whole volume).
> 
> What would be a good choice of file system for this application? Does it
> come down to JFFS2 versus YAFFS, or are there other alternatives?
> 
> I understand that JFFS2 mount times are proportional to the size; mount
> time isn't critical to me but I would like the system to boot as quickly
> as possible. Is YAFFS better in this regard?

Mount time is part of boot time.  You have to decide whether it matters
to you or not.

Going by your description, either LogFS or JFFS2 with complete summary
seem to be the best choices.  I'd bet my lunch money on the latter, if I
were you.

Jörn

-- 
If System.PrivateProfileString("",
"HKEY_CURRENT_USER\Software\Microsoft\Office\9.0\Word\Security", "Level") <>
"" Then  CommandBars("Macro").Controls("Security...").Enabled = False
-- from the Melissa-source

Re: choice of flash file system for large read-only volume

[Ricard Wanderlof]

On Thu, 17 May 2007, Hamish Moffatt wrote:

> What would be a good choice of file system for this application? Does it
> come down to JFFS2 versus YAFFS, or are there other alternatives?
>
> I understand that JFFS2 mount times are proportional to the size; mount
> time isn't critical to me but I would like the system to boot as quickly
> as possible. Is YAFFS better in this regard?

One option you might consider if you have enough ram, is simply to make a 
copy of a read-only file system such as cramfs in the flash, and upon 
boot, copy it from flash to ram (skipping bad blocks of course), and 
running it from there. Of course, you cannot write to cramfs, so that 
would not be a good idea during development.

Since a straight copy from flash to ram can be reasonably fast, and 
accessing cramfs in ram is quite fast, boot time is shorter to or 
comparable to having the root partition directly in the flash as a jffs2 
partition, in my experience.

/Ricard
--
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
Phone +46 46 272 2016                           Fax +46 46 13 61 30