Improving ext4: bigalloc, inline data, and metadata checksums

Posted Dec 4, 2011 6:17 UTC (Sun) by raven667 (subscriber, #5198)
In reply to: Improving ext4: bigalloc, inline data, and metadata checksums by dlang
Parent article: Improving ext4: bigalloc, inline data, and metadata checksums

I guess I was under the impression, incorrect it may be, that the concepts of write barriers were already baked into most responsible filesystems but that the support for working through LVM was recent (in the last 5yrs) and the support for actually issuing the right commands to the storage and having the storage respect them was also more recent. Maybe I'm wrong and barriers as a concept are newer.

In any event there is a bright line between how the kernel handles internal data structures and what the hardware does and for storage with battery backed write cache once an IO is posted to the storage it is as good as done so there is no need to ask the storage to commit its blocks in any particular fashion. The only issue is that the kernel issue the IO requests in a responsible manner.

Improving ext4: bigalloc, inline data, and metadata checksums

Posted Dec 4, 2011 6:41 UTC (Sun) by dlang (guest, #313) [Link] (8 responses)

barriers as a concept are not new, but your assumption that filesystems support them is the issue.

per the messages earlier in this thread, JFS does not, for a long time (even after it was the default in Fedora), LVM did not.

so barriers actually working correctly is relatively new (and very recently they have found more efficient ways to enforce ordering than the older version of barriers.

Improving ext4: bigalloc, inline data, and metadata checksums

Posted Dec 4, 2011 11:24 UTC (Sun) by tytso (subscriber, #9993) [Link]

JFS still to this day does not issues barriers / cache flushes.

It shouldn't be that hard to add support, but no one is doing any development work on it.

Improving ext4: bigalloc, inline data, and metadata checksums

Posted Dec 4, 2011 16:26 UTC (Sun) by rahulsundaram (subscriber, #21946) [Link] (6 responses)

JFS has never been default in Fedora.

Improving ext4: bigalloc, inline data, and metadata checksums

Posted Dec 4, 2011 16:50 UTC (Sun) by dlang (guest, #313) [Link] (5 responses)

I didn't think that I ever implied that it was.

Fedora has actually been rather limited in it's support of various filesystems. The kernel supports the different filesystems, but the installer hasn't given you the option of using XFS and JFS for your main filsystem for example.

Improving ext4: bigalloc, inline data, and metadata checksums

Posted Dec 4, 2011 17:41 UTC (Sun) by rahulsundaram (subscriber, #21946) [Link] (4 responses)

It appears you did

"JFS does not, for a long time (even after it was the default in Fedora)"

You are inaccurate about your claim on the installer as well. XFS is a standard option in Fedora for several releases ever since Red Hat hired Eric Sandeen from SGI to maintain it (and help develop Ext4). JFS is a non-standard option.

Improving ext4: bigalloc, inline data, and metadata checksums

Posted Dec 4, 2011 19:22 UTC (Sun) by dlang (guest, #313) [Link] (3 responses)

re: JFS, oops, I don't know what I was thinking when I typed that.

re: XFS, I've been using linux since '94, so XFS support in the installer is very recent :-)

I haven't been using Fedora for quite a while, my experiance to RedHat distros is mostly RHEL (and CentOS), which lag behind. I believe that RHEL5 still didn't support XFS in the installer

Improving ext4: bigalloc, inline data, and metadata checksums

Posted Dec 4, 2011 19:53 UTC (Sun) by rahulsundaram (subscriber, #21946) [Link]

"Very recent" is relative and not quite so accurate either. All versions of Fedora installer have supported XFS. You just had to pass "xfs" as a installer option. Same with jfs or reiserfs. Atleast Fedora 10 beta onwards supports XFS as a standard option without having to do anything

http://fedoraproject.org/wiki/Releases/10/Beta/ReleaseNot...

That is early 2008. RHEL 6 has xfs support as a add-on subscription and is supported within the installer as well IIRC.

Improving ext4: bigalloc, inline data, and metadata checksums

Posted Dec 5, 2011 16:15 UTC (Mon) by wookey (guest, #5501) [Link] (1 responses)

I think dlang meant this:
"..., for a long time (even after it was the default in Fedora), LVM did not"

(I parsed it the way rahulsundaram did too - it's not clear).

Improving ext4: bigalloc, inline data, and metadata checksums

Posted Dec 5, 2011 16:59 UTC (Mon) by dlang (guest, #313) [Link]

yes, now that you say that ir reminds me that I was meaning that for a long time after LVM was the default on Fedora, it didn't support barriers.

Improving ext4: bigalloc, inline data, and metadata checksums

Posted Jan 30, 2012 8:50 UTC (Mon) by sbergman27 (guest, #10767) [Link]

Old thread, I know. But why people are still talking about barriers I'm not sure. Abandoning the use of barriers was agreed upon at the 2010 Linux Filesystem Summit. And they completed their departure in 2.6.37, IIRC. Barriers are no more. They don't matter. They've been replaced by FUA, etc.