If the access performance of a file on the GFS Shared File System is getting low, the file data may be fragmented. In this case, change the amount of indirect extent management information of the file to improve the performance.
GFS Shared File System manages the file data with the extent-based allocation information. If the amount of extent consisting a file increases, the allocation information of file data will be stored on the indirect extent management information (IEX).
Meta-data server (MDS) reads IEX from the disk and caches it on memory to read or write the file data. However, the IEX cache overflows in the following cases and then the performance to read or update file data is degraded:
One file has a very great amount of extents.
Some files to be read or written at the same time have a very great amount of extents.
To avoid such circumstances, set the tuning parameter SFCFS_NCACHE_IEX to increase the amount of IEX cache.
See
For details on the tuning parameter SFCFS_NCACHE_IEX and how to set it, refer to "14.1.1 Amount of Cache" in this manual.
The following example shows how to estimate the amount of IEX cache.
If the access performance is getting low due to concurrent access of two files, /mnt/gfs01/fileA and /mnt/gfs01/fileB on the GFS Shared File system, use sfcextcount(1M) to check the number of IEX in these two files.
The values in the third field are the number of IEX.
# /etc/opt/FJSVgfs/bin/sfcextcount -f /mnt/gfs01/fileA /dev/sfdsk/gfs01/dsk/volume01 6: 81920 4724 # /etc/opt/FJSVgfs/bin/sfcextcount -f /mnt/gfs01/fileB /dev/sfdsk/gfs01/dsk/volume01 8: 98304 5668 |
See
For details on sfcextcount(1M), refer to "B.2.13 sfcextcount (1M) Outputs the extent information of the file." in this manual.
Calculate the total amount of IEX checked in step 1.
4724 + 5668 = 10392
Estimate the larger value than 10392 as the amount of IEX cache.
