Today, support for metadata journaling has been added to NetBSD's implementation of the Berkeley Fast File System (FFS), eliminating the need for lengthy file system checks after a crash or power failure. Support for converting existing file systems to use the new journaling capabilities is provided as well. See the official announcement
for all the details.
Post a Comment
Member since:
2005-07-24
Member since:2007-02-26
Soft updates were available and documented here: http://www.netbsd.org/docs/misc/#softdeps
Member since:2005-07-08
Yes...but not in the same way other people do journaling. Apparently they've metadata journaling - just like XFS, JFS or ext3 with the "data=writeback" mount option.
But if you only journal the metadata, you're only sure that the metadata is safe - not the data. IOW, you don't get metadata corruption (you don't need to fsck after a hard reboot), but the data of the file you were writting at the time of the reboot can be lost/corrupted. In XFS for example a file can get completely zeroed after a hard reboot.
There're two main ways to workaround this. One, journal the data (like in ext3 with the data=journal option) - but it's too slow. Second, write the data of a file before you journal its metadata, so that even in the event of a hard reboot, you are sure that the content of the file are not corrupted/lost - they may be outdated (the data was in ram and was not written to disk when the reboot happened), but not lost/corrupte (you may get a "corrupted" file in the sense that the process which was writting to it doesn't finishes writting what it was doing, but certainly you don't get rubbish). This is what ext3 does by default - it harms performance, but it's worth of it, specially for desktops.
You can also avoid completely the journaling, like zfs/btrfs do, but that's not really a "journaling mode"
Member since:2006-01-01
it says in the announcement to remove "softdep" if presnet.
Edited 2008-08-01 17:25 UTC
Member since:2005-11-18
Soft-updates and the log-structured filesystem (LFS). But soft-updates are fairly complex, and LFS does not have the same proven reliability as FFS. So, the addition of journaling to FFS is great, and a very nice contribution from Wasabi!
Member since:
2005-07-13
Member since:
2005-07-06
The whole debate of soft updates vs journaling, and the bragging of BSD dudes about soft updates being superior, is now enlightened with a whole new light.
Of course, I applaud NetBSD and Wasibi for offering this, and it's a Good Thing that the user can /choose/ between soft updates and journaling.
But what will be the default? Journaling or soft updates? And if it will be journaling, are the fs devs who advised journaling still to be taken serious?
Member since:2005-07-24
My understanding has been that soft-updates was a fairly complex feature to implement. More so than journaling. It may very well be that the maintenance overhead outweighed any possible technical advantages it may have had. The BSDs have always been a bit out in right field, in my opinion, on this issue.
Member since:2008-08-01
Member since:2005-07-24
There should be a default. Quivering in limbo is not proper installer behavior.
Edited 2008-08-02 02:17 UTC
Member since:2008-07-15
It's not "quivering in limbo," but rather the filesystem's default state is to have neither softdep nor journaling enabled and, depending on certain partition setups, this actually does make sense. Take, for example, a secure partition for applications, intended to be mounted read-only, and the partition archive/image is already created. The only thing that you intend to do with that partition is mount it rw, extract the archive, then mount it read-only from then on. In this case, you'd want to leave both softdep and journaling turned off. Sure, it takes about five seconds to go into /etc/fstab and get rid of the option, but if you know you're going to use that partition for a specific use where you know you won't need them, why have them enabled at all to start? Also, NetBSD is not a hand-holding system, period. It assumes you know what you're doing, it's defaults are barebones. The idea is that if you need something, you know you need it and will enable it yourself, either during the installation process or afterwards. Given this, it only makes sense that neither softdeps nor journaling is used by default, as it's not the filesystem's default state.
Member since:2005-07-06
sbergman27 was talking about a default. The default is currently to have no journaling AND no soft updates. IMHO, that's a bad choice. Having a "safe" default protects data. The scenarios you explained are valid, but users who know what they are doing will know how to turn it of for those special cases, and since it's only a few seconds editing fstab...
But the installer should default to something that protects data. Period.
Member since:2008-08-01
Member since:2005-07-06
If you are right, and the data is protected without soft updates and journaling, why the effort of adding them?
I'm not convinced yet.
Edit: OK, maybe you mean that those additions are only meant to shorten filesystem checks. I would agree with that. Still, fast filesystem recovery, when possible, is normally a default option for both desktops and servers. I remember Windows 98 blue start screens, scanning the FAT32 filesystem for 15 minutes. Windows 2000, with NTFS (journalled), booted fine, even after an unclean shutdown. Same goes for Linux with Ext3, it's mostly faster. All OS-es I know of default to enable the journaling. I don't see a compelling argument not to do it.
Edited 2008-08-02 11:46 UTC
Member since:2006-09-01
To check off a buzzword? They listened to user feedback? I'm sure there are people who need those features, and adding journalling keeps the people who do need it from jumping ship.
NetBSD fills the portable embedded system niche in the BSD universe. It's going to be installed on systems that don't necessarily need journalling or soft-updates on the system, or the systems don't have the resources to support them. Journalling takes up disk space and disk IO throughput takes a hit.
