search for: nocow

----- Forwarded Message ----- From: "Stefan Hajnoczi" <stefanha@redhat.com> To: "Eric Sandeen" <sandeen@redhat.com> Cc: virt-devel@redhat.com, "Kevin Wolf" <kwolf@redhat.com> Sent: Friday, November 22, 2013 9:20:51 AM Subject: [virt-devel] btrfs NOCOW for VM disk images Hi, In upstream QEMU we''re discussing patches that set the NOCOW flag on disk image files. We''re told that this increases btrfs performance greatly since the file system will modify data in-place like ext4/xfs. During testing I found that the NOCOW flag preve...

Add ''-C'' (nocow) option to vhd-util create. Btrfs has terrible performance when hosting VM images, even more when the guest in those VM are also using btrfs as file system. One way to mitigate this bad performance is to turn off COW attributes on VM files (since having copy on write for this kind of data is not u...

Hello, some time ago we discussed on #btrfs that the nocow attribute for files wasn''t working (around 3.3 or 3.4 kernels). That was evident by files fragmenting even with the attribute set. Chris mentioned to find a fix quickly for that, and posted some lines of change into irc. But recently someone mentioned that 3.6-rc looks like still not resp...

Hello, is it possible to set nodatacow on a per-file basis? I couldn''t find anything. If not, wouldn''t that be a great feature to get around the performance issues with VM and database storage? Of course cloning should still cause COW. Thanks, Ralf-Peter -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to

Balance will create reloc_root for each fs root, and it''s going to record last_snapshot to filter shared blocks. The side effect of setting last_snapshot is to break nocow attributes of files. So it turns out that checking last_snapshot does not always ensure that a node/leaf/file_extent is shared. That''s why shared node/leaf needs to search extent tree for number of references even after having checked last_snapshot, and updating fs/file tree works top-do...

I set the C (NOCOW) and z (Not_Compressed) flags on a folder but the extent counts of files contained there keep increasing. Said files are large and frequently modified but not changing in size. This does not happen when the filesystem is mounted with nodatacow. I''m using this as a workaround since subvolu...

What happens if you set an individual file inside a subvolume as nocow (chattr +C) and then take a snapshot of that subvolume and modify the file in both? Will btrfs now ignore the nocow attribute completely or will it do "as few copies as possible"? (I''d love to know if it''s possible to visualize the fragmentation of a single file.) -- To...

I want to eliminate the COW feature on all of my OS files. It is a nice feature for user files, but I don''t see a clear benefit for the actual OS files. And I suspect that COW induced fragmentation is causing or aggravating problems with my system including the boot open_ctree problem. I had planned to recursively chattr these files to "nodatacow" status but then I ran

Hello, This patch simplifies the nodatacow checker. If all references were created after the latest snapshot, then we can avoid COW safely. This patch also updates run_delalloc_nocow to do more fine-grained checking. Regards Signed-off-by: Yan Zheng <zheng.yan@oracle.com> --- diff -urp 3/fs/btrfs/ctree.h 4/fs/btrfs/ctree.h --- 3/fs/btrfs/ctree.h 2008-10-27 16:31:51.000000000 +0800 +++ 4/fs/btrfs/ctree.h 2008-10-27 16:34:27.000000000 +0800 @@ -445,6 +445,7 @@ struct btr...

The rule originally comes from nocow writing, but snapshot-aware defrag is a different case, the extent has been writen and we''re not going to change the extent but add a reference on the data. So we''re able to allow such compressed extents to be merged into one bigger extent if they''re pointing to the same...

...it comes to VM images. This is mitigated if you set xattr +C at image create time (it must be zero length file for +C to take). But if you cp --reflink or snapshot the containing subvolume, then COW starts to happen for new writes to either copy; overwrites to either copies newly written blocks are nocow. So anyway you can quickly get into complicated states with VM images on Btrfs. I'm not sure of the long term plan. This is how to set xattr +C at qcow2 create time, only applicable when the qcow2 is on Btrfs. # qemu-img create -o nocow=on But really piles more testing is needed to better un...

...06,17 @@ TRACE_EVENT(btrfs_get_extent, __entry->refs, __entry->compress_type) ); -#define show_ordered_flags(flags) \ - __print_symbolic(flags, \ - { BTRFS_ORDERED_IO_DONE, "IO_DONE" }, \ - { BTRFS_ORDERED_COMPLETE, "COMPLETE" }, \ - { BTRFS_ORDERED_NOCOW, "NOCOW" }, \ - { BTRFS_ORDERED_COMPRESSED, "COMPRESSED" }, \ - { BTRFS_ORDERED_PREALLOC, "PREALLOC" }, \ - { BTRFS_ORDERED_DIRECT, "DIRECT" }, \ - { BTRFS_ORDERED_IOERR, "IOERR" }, \ - { BTRFS_ORDERED_UPDATED_ISIZE, "UPDATED_...

What are the recommendations for running KVM images on BTRFS systems using kernel 3.4?  I saw older posts on the web complaining about poor performance, but I know a lot of work has gone into btrfs since then.  There also seemed to be the nocow option, but I didn''t find anything that said it actualy helped. Anybody have ideas? Thanks, Matt -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majord...

I have a 3 disk raid1 filesystem mounted with nodatacow. I have a folder in said filesystem with the ''C'' NOCOW & ''Z'' Not_Compressed flags set for good measure. I then copy in a large file and proceed to make random modifications. Filefrag shows no additional extents created, good so far. A big thank you to the those devs who got that working. However, after a balance run (which crashed...

...d or some other tool and rest assured that the blocks which contained the sensitive information have been wiped. However on btrfs it would seem any such attempt would write the zeros/random data to a new location, leaving the old blocks with the sensitive data intact. Further, since specifying NOCOW is only possible for newly created files, there seems to be no way to overwrite the appropriate blocks short of deleting the associated file and then filling the entire free filesystem space with zeros/random data such that the old blocks are eventually overwritten. What''s the verdict...

...fs tasks peeking at 7-8M/s, namely: btrfs-endio-wri btrfs-delayed-m btrfs-transacti btrfs-cleaner I''ve already tracked down some sub-optimal performance to the fact I''m hosting a large number of RRDs which I''ve attempted to mitigate with moving them to a nocow sub-volume and performing the appropriate chattr magic on the host directories. However I''m still seeing these spikes occur at seemingly random times. My next suspect is our build directories which contain about 400Mb of build artefacts that are shuffled around each build. However before...

...fff880118a31000 ffff880115f88638 ffff88001f438448 [ 68.127480] Call Trace: [ 68.127508] [<ffffffffa0482f29>] ? release_extent_buffer+0xa9/0xd0 [btrfs] [ 68.127553] [<ffffffffa048862f>] ? free_extent_buffer+0x4f/0xa0 [btrfs] [ 68.127598] [<ffffffffa04716d6>] run_delalloc_nocow+0x436/0xaf0 [btrfs] [ 68.127641] [<ffffffffa0472180>] run_delalloc_range+0x320/0x390 [btrfs] [ 68.127685] [<ffffffffa04854c1>] ? find_lock_delalloc_range.constprop.44+0x1d1/0x1f0 [btrfs] [ 68.127735] [<ffffffffa0487044>] __extent_writepage+0x354/0x7b0 [btrfs] [ 68.12777...

I just pushed some code into the compiz repository for initial metacity theme support. It's not complete, left and right borders are not rendered correctly, button decorations doesn't always match event window locations, maximized and shaded windows are not rendered as when running metacity, button locations are not configurable as with metacity... but it still seem to look OK with most

The Wiki does not make it clear as to why adding a secondary device defaults to RAID1 metadata and RAID0 data. I bought two SSDs with the intention of doing a BTRFS RAID0 for my root. What is the difference between forcing RAID0 on metadata and data as opposed to the default behavior? Can anyone clarify that? Thank you for your time, Mario -- To unsubscribe from this list: send the line

Hello list, i know what btrfs don''t support swap files. I read arch wiki and when i reading about systemd addon for auto create swapfile on btrfs, i invent the way, how create and using swap file, just see following sh code: swapfile=$(losetup -f) #free loop device truncate -s 8G /swap #create 8G sparse swap file losetup $swapfile /swap #mount file to loop mkswap $swapfile swapon