[#LU-11466] DoM files should not need LSOM sync for valid attributes on the MDS

Currently, Lazy size on MDT (LSOM) creates and stores file attributes on the MDS for Data on MDT files, just like all other files, and we need to llsom_sync to get the file attributes for DoM files to be correct. The file metadata for DoM files is on the MDS already and is valid. Thus, we shouldn’t have to sync to get the LSOM data to match the DoM file metadata.

From the example below, we can see that the number of blocks in the LSOM data for the DoM file mdt_file_2 is only updated after we run llsom_sync

# lfs setstripe -E 4M -L mdt /lustre/scratch/mdt_file_2
# dd if=/dev/urandom of=/lustre/scratch/mdt_file_2 bs=25k count=2
2+0 records in
2+0 records out
51200 bytes (51 kB) copied, 0.00100831 s, 50.8 MB/s

# lfs getsom /lustre/scratch/mdt_file_2
file: /lustre/scratch/mdt_file_2 size: 51200 blocks: 0 flags: 4

# llsom_sync /lustre/scratch -vvvv -vvv -u cl1 -m scratch-MDT0000
Start receiving records
Processed changelog record index:5894 type:CREAT(0x1) FID:[0x200000401:0x99d:0x0]
Processed changelog record index:5895 type:LYOUT(0xc) FID:[0x200000401:0x99d:0x0]
Processed changelog record index:5896 type:XATTR(0xf) FID:[0x200000401:0x99d:0x0]
Processed changelog record index:5897 type:CLOSE(0xb) FID:[0x200000401:0x99d:0x0]
Start to sync 1 records.
record 1652041866429631028:5897, updated LSOM for fid [0x200000401:0x99d:0x0] size:51200 blocks:112
Processed changelog record index:5898 type:CLOSE(0xb) FID:[0x200000401:0x99d:0x0]
Start to sync 1 records.
record 1652041866429970184:5898, updated LSOM for fid [0x200000401:0x99d:0x0] size:51200 blocks:112
Processed changelog record index:5909 type:XATTR(0xf) FID:[0x200000401:0x99d:0x0]
Processed changelog record index:5910 type:XATTR(0xf) FID:[0x200000401:0x99d:0x0]
Processed changelog record index:5911 type:CLOSE(0xb) FID:[0x200000401:0x99d:0x0]
Start to sync 1 records.
record 1652041916629724290:5911, updated LSOM for fid [0x200000401:0x99d:0x0] size:51200 blocks:112
finished reading [scratch-MDT0000]
Start to sync 0 records.
[root@trevis-62vm4 ~]# lfs getsom /lustre/scratch/mdt_file_2
file: /lustre/scratch/mdt_file_2 size: 51200 blocks: 112 flags: 4

Also, for DoM files, shouldn’t the flag = 1; SOM_FL_STRICT = 0x0001 - Known strictly correct, FLR or DoM file (SoM guaranteed). In the case above, the flag never changes from 4, SOM_FL_LAZY = 0x0004 - Approximate, may never have been strictly correct, need to sync SOM data to achieve eventual consistency.

[LU-11466] DoM files should not need LSOM sync for valid attributes on the MDS Created: 03/Oct/18 Updated: 12/Oct/19 Resolved: 27/Nov/18
Status:	Resolved
Project:	Lustre
Component/s:	None
Affects Version/s:	Lustre 2.12.0
Fix Version/s:	Lustre 2.12.0

[LU-11466] DoM files should not need LSOM sync for valid attributes on the MDS Created: 03/Oct/18 Updated: 12/Oct/19 Resolved: 27/Nov/18