[gpfsug-discuss] subblock sanity check in 5.0

[Sven Oehme]

Joseph,

the subblocksize will be derived from the smallest blocksize in the
filesytem, given you specified a metadata block size of 512k thats what
will be used to calculate the number of subblocks, even your data pool is
4mb.
is this setup for a traditional NSD Setup or for GNR as the recommendations
would be different.

sven

On Tue, Jun 26, 2018 at 2:59 AM Joseph Mendoza <jam at ucar.edu> wrote:

> 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
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