Joey, The subblocks-per-full-block value cannot be specified when the file system is created, but is rather computed automatically by GPFS. In file systems with format older than 5.0, the value is fixed at 32. For file systems with format 5.0.0 or later, the value is computed based on the block size. See manpage for mmcrfs, in table where the -B BlockSize option is explained. (Table 1. Block sizes and subblock sizes) . Say, for the default (in 5.0+) 4MB block size, the subblock size is 8KB.
The minimum "practical" subblock size is 4KB, to keep 4KB-alignment to accommodate 4KN devices. Felipe ---- Felipe Knop [email protected] GPFS Development and Security IBM Systems IBM Building 008 2455 South Rd, Poughkeepsie, NY 12601 (845) 433-9314 T/L 293-9314 From: Joseph Mendoza <[email protected]> To: gpfsug main discussion list <[email protected]> Date: 06/25/2018 08:59 PM Subject: [gpfsug-discuss] subblock sanity check in 5.0 Sent by: [email protected] Quick question, anyone know why GPFS wouldn't respect the default for the subblocks-per-full-block parameter when creating a new filesystem? I'd expect it to be set to 512 for an 8MB block size but my guess is that also specifying a metadata-block-size is interfering with it (by being too small). This was a parameter recommended by the vendor for a 4.2 installation with metadata on dedicated SSDs in the system pool, any best practices for 5.0? I'm guessing I'd have to bump it up to at least 4MB to get 512 subblocks for both pools. fs1 created with: # mmcrfs fs1 -F fs1_ALL -A no -B 8M -i 4096 -m 2 -M 2 -r 1 -R 2 -j cluster -n 9000 --metadata-block-size 512K --perfileset-quota --filesetdf -S relatime -Q yes --inode-limit 20000000:10000000 -T /gpfs/fs1 # mmlsfs fs1 <snipped> flag value description ------------------- ------------------------ ----------------------------------- -f 8192 Minimum fragment (subblock) size in bytes (system pool) 131072 Minimum fragment (subblock) size in bytes (other pools) -i 4096 Inode size in bytes -I 32768 Indirect block size in bytes -B 524288 Block size (system pool) 8388608 Block size (other pools) -V 19.01 (5.0.1.0) File system version --subblocks-per-full-block 64 Number of subblocks per full block -P system;DATA Disk storage pools in file system Thanks! --Joey Mendoza NCAR _______________________________________________ gpfsug-discuss mailing list gpfsug-discuss at spectrumscale.org http://gpfsug.org/mailman/listinfo/gpfsug-discuss
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