Bug #61151
openlibcephfs: incorrectly showing the size for snapshots when stating them
Added by Xiubo Li 12 months ago. Updated 12 months ago.
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Description
If the rstat is enabled for the .snap snapdir it should report the total size for all the snapshots. And at the same time for each snapshot it should report the rstat size when making the snapshot.
Currently it will always show the current parent dir's rstat, which is incorrect.
Updated by Greg Farnum 12 months ago
If the rstat is enabled for the .snap snapdir it should report the total size for all the snapshots.
I'm not sure about this. The total size of all snapshots is a pretty meaningless number, isn't it? If there's 10GB of data in a directory, and we snapshot it 10 times without changing any data, we get 10 user-visible snapshots that take up a total of 10GB of space on disk. But the MDS can't actually see how much space the OSDs are using — it doesn't have that information reported. So all it could really report for total size is 100GB, right?
But any user who sees that would expect to free up 10GB of space by deleting one of those ten snapshots, which also won't happen...So I don't think that's a great UX option. :/
Updated by Xiubo Li 12 months ago
The tests worked as expected:
[xiubli@ceph libcephfs]$ mkdir dir2 [xiubli@ceph libcephfs]$ stat dir2/.snap/ File: dir2/.snap/ Size: 0 Blocks: 1 IO Block: 4096 directory Device: 2ah/42d Inode: 282574488338941 Links: 2 Access: (0755/drwxr-xr-x) Uid: ( 1000/ xiubli) Gid: ( 1000/ xiubli) Access: 2023-05-22 16:45:10.198927211 +0800 Modify: 2023-05-22 13:24:26.720969831 +0800 Change: 2023-05-22 13:24:26.720969831 +0800 Birth: - [xiubli@ceph libcephfs]$ dd if=/dev/random of=./dir2/file1111 bs=1K count=1 1+0 records in 1+0 records out 1024 bytes (1.0 kB, 1.0 KiB) copied, 0.0140872 s, 72.7 kB/s [xiubli@ceph libcephfs]$ stat dir2/.snap/ File: dir2/.snap/ Size: 0 Blocks: 1 IO Block: 4096 directory Device: 2ah/42d Inode: 282574488338941 Links: 2 Access: (0755/drwxr-xr-x) Uid: ( 1000/ xiubli) Gid: ( 1000/ xiubli) Access: 2023-05-22 16:45:10.198927211 +0800 Modify: 2023-05-22 13:24:26.720969831 +0800 Change: 2023-05-22 13:24:26.720969831 +0800 Birth: - [xiubli@ceph libcephfs]$ ll -h dir2/ total 1.0K -rw-r--r-- 1 xiubli xiubli 1.0K May 22 16:45 file1111 [xiubli@ceph libcephfs]$ mkdir dir2/.snap/snapshot1 [xiubli@ceph libcephfs]$ stat dir2/.snap/ File: dir2/.snap/ Size: 1024 Blocks: 1 IO Block: 4096 directory Device: 2ah/42d Inode: 282574488338941 Links: 2 Access: (0755/drwxr-xr-x) Uid: ( 1000/ xiubli) Gid: ( 1000/ xiubli) Access: 2023-05-22 16:45:10.198927211 +0800 Modify: 2023-05-22 16:46:27.430254821 +0800 Change: 2023-05-22 16:46:27.430254821 +0800 Birth: - [xiubli@ceph libcephfs]$ stat dir2/.snap/snapshot1/ File: dir2/.snap/snapshot1/ Size: 1024 Blocks: 1 IO Block: 4096 directory Device: 2ah/42d Inode: 564049465049597 Links: 2 Access: (0755/drwxr-xr-x) Uid: ( 1000/ xiubli) Gid: ( 1000/ xiubli) Access: 2023-05-22 16:45:10.198927211 +0800 Modify: 2023-05-22 16:45:54.545237972 +0800 Change: 2023-05-22 16:46:27.430254821 +0800 Birth: - [xiubli@ceph libcephfs]$ stat dir2/.snap/snapshot1/file1111 File: dir2/.snap/snapshot1/file1111 Size: 1024 Blocks: 2 IO Block: 4194304 regular file Device: 2ah/42d Inode: 564049465049598 Links: 1 Access: (0644/-rw-r--r--) Uid: ( 1000/ xiubli) Gid: ( 1000/ xiubli) Access: 2023-05-22 16:45:54.545237972 +0800 Modify: 2023-05-22 16:45:54.583346799 +0800 Change: 2023-05-22 16:45:54.583346799 +0800 Birth: - [xiubli@ceph libcephfs]$ dd if=/dev/random of=./dir2/file2222 bs=1K count=1 1+0 records in 1+0 records out 1024 bytes (1.0 kB, 1.0 KiB) copied, 0.00332263 s, 308 kB/s [xiubli@ceph libcephfs]$ stat dir2/.snap/snapshot1/ File: dir2/.snap/snapshot1/ Size: 1024 Blocks: 1 IO Block: 4096 directory Device: 2ah/42d Inode: 564049465049597 Links: 2 Access: (0755/drwxr-xr-x) Uid: ( 1000/ xiubli) Gid: ( 1000/ xiubli) Access: 2023-05-22 16:45:10.198927211 +0800 Modify: 2023-05-22 16:45:54.545237972 +0800 Change: 2023-05-22 16:46:27.430254821 +0800 Birth: - [xiubli@ceph libcephfs]$ stat dir2/.snap/snapshot1/file1111 File: dir2/.snap/snapshot1/file1111 Size: 1024 Blocks: 2 IO Block: 4194304 regular file Device: 2ah/42d Inode: 564049465049598 Links: 1 Access: (0644/-rw-r--r--) Uid: ( 1000/ xiubli) Gid: ( 1000/ xiubli) Access: 2023-05-22 16:45:54.545237972 +0800 Modify: 2023-05-22 16:45:54.583346799 +0800 Change: 2023-05-22 16:45:54.583346799 +0800 Birth: - [xiubli@ceph libcephfs]$ mkdir dir2/.snap/snapshot2 [xiubli@ceph libcephfs]$ stat dir2/.snap/ File: dir2/.snap/ Size: 3072 Blocks: 1 IO Block: 4096 directory Device: 2ah/42d Inode: 282574488338941 Links: 2 Access: (0755/drwxr-xr-x) Uid: ( 1000/ xiubli) Gid: ( 1000/ xiubli) Access: 2023-05-22 16:45:10.198927211 +0800 Modify: 2023-05-22 16:48:15.306613624 +0800 Change: 2023-05-22 16:48:15.306613624 +0800 Birth: - [xiubli@ceph libcephfs]$ stat dir2/.snap/snapshot2/ File: dir2/.snap/snapshot2/ Size: 2048 Blocks: 1 IO Block: 4096 directory Device: 2ah/42d Inode: 845524441760253 Links: 2 Access: (0755/drwxr-xr-x) Uid: ( 1000/ xiubli) Gid: ( 1000/ xiubli) Access: 2023-05-22 16:45:10.198927211 +0800 Modify: 2023-05-22 16:46:45.947429018 +0800 Change: 2023-05-22 16:48:15.306613624 +0800 Birth: - [xiubli@ceph libcephfs]$ dd if=/dev/random of=./dir2/file3333 bs=1K count=1 1+0 records in 1+0 records out 1024 bytes (1.0 kB, 1.0 KiB) copied, 0.0030967 s, 331 kB/s [xiubli@ceph libcephfs]$ stat dir2/.snap/ File: dir2/.snap/ Size: 3072 Blocks: 1 IO Block: 4096 directory Device: 2ah/42d Inode: 282574488338941 Links: 2 Access: (0755/drwxr-xr-x) Uid: ( 1000/ xiubli) Gid: ( 1000/ xiubli) Access: 2023-05-22 16:45:10.198927211 +0800 Modify: 2023-05-22 16:48:15.306613624 +0800 Change: 2023-05-22 16:48:15.306613624 +0800 Birth: - [xiubli@ceph libcephfs]$ mkdir dir2/.snap/snapshot3 [xiubli@ceph libcephfs]$ stat dir2/.snap/ File: dir2/.snap/ Size: 6144 Blocks: 1 IO Block: 4096 directory Device: 2ah/42d Inode: 282574488338941 Links: 2 Access: (0755/drwxr-xr-x) Uid: ( 1000/ xiubli) Gid: ( 1000/ xiubli) Access: 2023-05-22 16:45:10.198927211 +0800 Modify: 2023-05-22 16:50:24.724830748 +0800 Change: 2023-05-22 16:50:24.724830748 +0800 Birth: - [xiubli@ceph libcephfs]$ stat dir2/.snap/snapshot3/ File: dir2/.snap/snapshot3/ Size: 3072 Blocks: 1 IO Block: 4096 directory Device: 2ah/42d Inode: 1126999418470909 Links: 2 Access: (0755/drwxr-xr-x) Uid: ( 1000/ xiubli) Gid: ( 1000/ xiubli) Access: 2023-05-22 16:45:10.198927211 +0800 Modify: 2023-05-22 16:48:45.221649134 +0800 Change: 2023-05-22 16:50:24.724830748 +0800 Birth: - [xiubli@ceph libcephfs]$ rmdir dir2/.snap/snapshot1/ [xiubli@ceph libcephfs]$ stat dir2/.snap/ File: dir2/.snap/ Size: 5120 Blocks: 1 IO Block: 4096 directory Device: 2ah/42d Inode: 282574488338941 Links: 2 Access: (0755/drwxr-xr-x) Uid: ( 1000/ xiubli) Gid: ( 1000/ xiubli) Access: 2023-05-22 16:45:10.198927211 +0800 Modify: 2023-05-22 16:50:56.561229503 +0800 Change: 2023-05-22 16:50:56.561229503 +0800 Birth: -
Updated by Xiubo Li 12 months ago
- Copied to Bug #61331: libcephfs: incorrectly showing the size for snapshots when stating them added
Updated by Xiubo Li 12 months ago
Greg Farnum wrote:
If the rstat is enabled for the .snap snapdir it should report the total size for all the snapshots.
I'm not sure about this. The total size of all snapshots is a pretty meaningless number, isn't it? If there's 10GB of data in a directory, and we snapshot it 10 times without changing any data, we get 10 user-visible snapshots that take up a total of 10GB of space on disk. But the MDS can't actually see how much space the OSDs are using — it doesn't have that information reported. So all it could really report for total size is 100GB, right?
Yeah, sounds reasonable, the total size of the snapshots in the snapdir couldn't represent the total disk spaces the snapshots used.
But any user who sees that would expect to free up 10GB of space by deleting one of those ten snapshots, which also won't happen...So I don't think that's a great UX option. :/
Let's show the total snapshot numbers always here instead ?
And also we should document about this somewhere. Because the snapshots may share the same Objects in backend Rados, so just removing one snapshot also won't make sure we can free the corresponding size of disk spaces.