choice of flash file system for large read-only volume
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
Signature · 1 line
Hamish Moffatt VK3SB <[email protected]> <[email protected]>
Quoted 3 lines · Hamish Moffatt
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. :)
Quoted 6 lines
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).
Quoted 6 lines
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
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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
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Ricard Wolf Wanderlöf ricardw(at)axis.com
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