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Author Topic: Why it takes so long to mount the onboard nand fs?  (Read 2739 times)
rc3
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« on: July 06, 2009, 02:41:13 PM »

This is something really bugging me: why it takes ages to mount an on-board nand memory on sheevaplug (also true on openrd client, so it seems it's filesystem type related)? It takes at least half a minute, if not a full minute, to mount a nand partition. Can someone exaplain a bit on this? Thanks.
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restamp
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« Reply #1 on: July 06, 2009, 03:23:09 PM »

I'm not sure there isn't more involved here -- a minute sounds like a long time -- but my understanding is that, by its nature, a jffs2 file system has to be completely scanned prior to being mounted.  Every block needs to be read.  This is necessary in order to detect and archive the bad blocks (or whatever you call the bad segments), and to create a pointer table to the free blocks and file system contents.  So it is inherently a slow process, and one that doesn't scale particularly well as NAND devices become larger.  That's one advantage to moving to the ubifs file system.

I'm speculating, but perhaps reading the NAND via whatever mechanism the mount command uses is less efficient than however the kernel deals with it when mounting it as the rootfs?

BTW, can someone explain to me how to mount the NAND after running the alpha6 installer?  It's not really a jffs2 FS anymore, but something that resides over the UBI layer.  I use an SDcard for the root fs here, and have no idea how to access the NAND from this configuration -- not that it's a pressing problem; it's more a matter of curiosity.
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semery
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« Reply #2 on: July 07, 2009, 11:38:17 AM »

Quote
This is something really bugging me: why it takes ages to mount an on-board nand memory on sheevaplug (also true on openrd client, so it seems it's filesystem type related)? It takes at least half a minute, if not a full minute, to mount a nand partition. Can someone exaplain a bit on this? Thanks.

See more info here:
http://www.plugcomputer.org/plugwiki/index.php/Enabling_UBIFS#Why_UBIFS_instead_of_JFFS2.3F

Quote
BTW, can someone explain to me how to mount the NAND after running the alpha6 installer?  It's not really a jffs2 FS anymore, but something that resides over the UBI layer.  I use an SDcard for the root fs here, and have no idea how to access the NAND from this configuration -- not that it's a pressing problem; it's more a matter of curiosity.

Answered here:
http://plugcomputer.org/plugforum/index.php?topic=478.msg2838#msg2838
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rc3
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« Reply #3 on: July 07, 2009, 12:32:57 PM »

Very useful information! Thanks semery. I tried ubifs with the built-in kernel on the openrd and it's way faster (at least in booting). I'm compiling 2.6.30 kernel with ubifs support and see how it goes.
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Rabeeh Khoury
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« Reply #4 on: July 08, 2009, 10:19:21 AM »

You can use the sheevaplug installer which uses ubifs.
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