Ext4 to be standard for Fedora 11, Btrfs also included (heise online) [LWN.net]

Ext4 to be standard for Fedora 11, Btrfs also included (heise online)

Posted Jan 23, 2009 21:31 UTC (Fri) by martinfick (subscriber, #4455)
In reply to: Ext4 to be standard for Fedora 11, Btrfs also included (heise online) by dlang
Parent article: Ext4 to be standard for Fedora 11, Btrfs also included (heise online)

I think my whole point must have gone right over your head? :)

Even my old drives do bad block remapping, but there is no way to know about it until they run out since they do not have SMART!! Given enough time, they will run out or the drive will crash entirely. I have older drives that do remap blocks, but have run out of spare blocks. I no longer use them since they are obviously risky to use, but in the meantime I am happy to have not lost any data until I realized the problem.

Your OS point is idealistic as I tried to explain previously. I don't know of any linux distro that enables smartmon by default, so, no, the average user will not know when the drive is going bad even thought the tools exists to find out. Even if they did have smartmon enabled, do you think the average user looks through logs to see if there are any problems? How would a linux desktop GUI only user ever know?

Not to mention, that you still have not provided a logical reason to NOT perform bad block allocation except for your stance that it is not really needed.

Just to add to this, my personal opinion is that the HD is the wrong place for this feature anyway. It requires you to waste an arbitrary number of blocks as spares. There is no way to get that number right, either you will have allocated too many or too few. Neither case is ideal. Since this really is a software feature (remapping), let the OS know and don't pretend it's a hardware feature. To be honest, it probably belongs at the block layer since it will not make sense to do it at the FS layer if using LVM.

Perhaps LVM should take care of this? If I use LVM, I should be able to have my spare blocks on a separate disk. In fact LVM should probably have thresholds that make it remap the entire disk when it starts to see too many bad blocks! I guess ideally all the layers should be able to handle badblocks somehow. :)

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Ext4 to be standard for Fedora 11, Btrfs also included (heise online)

Posted Jan 23, 2009 22:03 UTC (Fri) by dlang (✭ supporter ✭, #313) [Link]

one point, when a bad block gets remapped, you do (stand a very good chance that you) loose the data on that block.

the problem with having the OS do bad-block mapping is that people use drives with different OS's, and they would all have to know about all the bad blocks, what they were remapped to, etc.

drives used to work this way, the reliability of having the OS do this (even in cases where you weren't dual-booting) was bad enough that at the time it migrated into the drives so that the OS could forget about this, everyone considered this a step forward.

it's far more complicated for the drive to do the remapping than to let the OS do it, so it wasn't just a whim that change things so that every drive manufactured does it internally.

Ext4 to be standard for Fedora 11, Btrfs also included (heise online)

Posted Jan 24, 2009 13:36 UTC (Sat) by nix (subscriber, #2304) [Link]

Yes: but you can see bad blocks appear before any spares have been used at
all, if you only saw them on read, rather than after a rewrite.

Ext4 to be standard for Fedora 11, Btrfs also included (heise online)

Posted Jan 24, 2009 13:51 UTC (Sat) by dlang (✭ supporter ✭, #313) [Link]

but in that case the correct action isn't to mark the sector as bad, but to try to write to it (so that the sector will be remapped)

however, if the drive really is going bad, doing so could further damage your data