Re: [patch] ext2/3: document conditions when reliable operation ispossible

From: david
Date: Tue Aug 25 2009 - 19:04:22 EST

On Wed, 26 Aug 2009, Pavel Machek wrote:

I don't object to making that general statement - "Don't hot unplug a
device with an active file system or actively used raw device" - but
would object to the overly general statement about ext3 not working on
flash, RAID5 not working, etc...

You can object any way you want, but running ext3 on flash or MD RAID5
is stupid:

* ext2 would be faster

* ext2 would provide better protection against powerfail.

Not true in the slightest, you continue to ignore the ext2/3/4 developers
telling you that it will lose data.

I know I will lose data. Both ext2 and ext3 will lose data on
flashdisk. (That's what I'm trying to document). But... what is the
benefit of ext3 journaling on MD RAID5? (On flash, ext3 at least
protects you against kernel panic. MD RAID5 is in software, so... that
additional protection is just not there).

the block device can loose data, it has absolutly nothing to do with the filesystem

"ext3 works on flash and MD RAID5, as long as you do not have
powerfail" seems to be the accurate statement, and if you don't need
to protect against powerfails, you can just use ext2.

Strange how your personal preference is totally out of sync with the
entire enterprise class user base.

Perhaps noone told them MD RAID5 is dangerous? You see, that's exactly
what I'm trying to document here.

a MD raid array that's degraded to the point where there is no redundancy is dangerous, but I don't think that any of the enterprise users would be surprised.

I think they will be surprised that it's possible that a prior failed write that hasn't been scrubbed can cause data loss when the array later degrades.

David Lang
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at