I know this will be very confusing, but the code works different than one would think (not sure this is documented anywhere). The number of subblocks across pools of a fileystsem is calculated based on the smallest pools blocksize.
So given you have a 1MB blocksize in the system pool you will end up with 128 subblocks, now you have a 2nd pool (data) which will inherit the 128 subblocks and the code calculates a subblock size of 128k (16M/128=128k). Sven From: <[email protected]> on behalf of "Caubet Serrabou Marc (PSI)" <[email protected]> Reply-To: gpfsug main discussion list <[email protected]> Date: Tuesday, March 26, 2019 at 8:46 AM To: gpfsug main discussion list <[email protected]> Subject: [gpfsug-discuss] GPFS v5: Blocksizes and subblocks Hi all, according to several GPFS presentations as well as according to the man pages: Table 1. Block sizes and subblock sizes +-------------------------------+-------------------------------+ | Block size | Subblock size | +-------------------------------+-------------------------------+ | 64 KiB | 2 KiB | +-------------------------------+-------------------------------+ | 128 KiB | 4 KiB | +-------------------------------+-------------------------------+ | 256 KiB, 512 KiB, 1 MiB, 2 | 8 KiB | | MiB, 4 MiB | | +-------------------------------+-------------------------------+ | 8 MiB, 16 MiB | 16 KiB | +-------------------------------+-------------------------------+ A block size of 8MiB or 16MiB should contain subblocks of 16KiB. However, when creating a new filesystem with 16MiB blocksize, looks like is using 128KiB subblocks: [root@merlindssio01 ~]# mmlsfs merlin 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 . . . -n 128 Estimated number of nodes that will mount file system -B 1048576 Block size (system pool) 16777216 Block size (other pools) . . . What am I missing? According to documentation, I expect this to be a fixed value, or it isn't at all? On the other hand, I don't really understand the concept 'Indirect block size in bytes', can somebody clarify or provide some details about this setting? Thanks a lot and best regards, Marc _________________________________________ Paul Scherrer Institut High Performance Computing Marc Caubet Serrabou Building/Room: WHGA/019A Forschungsstrasse, 111 5232 Villigen PSI Switzerland Telephone: +41 56 310 46 67 E-Mail: [email protected] _______________________________________________ gpfsug-discuss mailing list gpfsug-discuss at spectrumscale.org http://gpfsug.org/mailman/listinfo/gpfsug-discuss
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