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Ext4 to be standard for Fedora 11, Btrfs also included (heise online)Ext4 to be standard for Fedora 11, Btrfs also included (heise online)Posted Jan 23, 2009 20:31 UTC (Fri) by dlang (✭ supporter ✭, #313)In reply to: Ext4 to be standard for Fedora 11, Btrfs also included (heise online) by martinfick Parent article: Ext4 to be standard for Fedora 11, Btrfs also included (heise online)
when did you last purchase a drive that doesn't do bad-block remapping?
The users don't need to know about SMART, they need to know that if the OS ever sees a bad block on the drive that the drive should be replaced. It hasn't been the case for _many_ years that it was normal to have some number of user-visible bad blocks on a drive. you almost have to go back to the days of MFM/RLL/ESDI drives (I think this was 12+ years ago)
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Ext4 to be standard for Fedora 11, Btrfs also included (heise online) Posted Jan 23, 2009 21:31 UTC (Fri) by martinfick (subscriber, #4455) [Link]
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. :)
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 12:43 UTC (Sat) by Los__D (guest, #15263) [Link]
When the spares runs out, the drive should be replaced immediately, if you care about your data.
No OS bad block remapping scheme will change that.
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
Ext4 to be standard for Fedora 11, Btrfs also included (heise online) Posted Jan 23, 2009 23:58 UTC (Fri) by nix (subscriber, #2304) [Link]
If the OS sees a bad block on a drive *after a write* the drive should be
replaced. If it's just a read, then the drive hasn't had a chance to do any bad block remapping yet, so nothing unexpected is going on.
(Using RAID will let you do that rewrite without losing the data that was
Ext4 to be standard for Fedora 11, Btrfs also included (heise online) Posted Jan 24, 2009 1:08 UTC (Sat) by EzDi (guest, #56297) [Link]
Exactly, I've had this problem with several drives where I get a bad sector somewhere, often underneath swap, a journal, or some other file system bit, because that's what's being dealt with before the incident that caused it.
Drives often don't remap UNTIL YOU DO A WRITE. So I keep getting errors while trying to mount, fsck, or when doing something to an adjacent sector, until I manually zero out that sector. Then my hard drive is perfect again from the OS's viewpoint.
Of course using bad block lists can often not do the right thing, because they only do a read test...
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