Maximum number of files in GPFS

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In GPFS we can configure a maximum number of inodes setting per fileset. This value can be online increased/decreased as needed, but never lower than the to the number of allocated inodes in the fileset. The maximum number of files (inodes) in a GPFS file system is documented to be:

https://www.ibm.com/docs/en/storage-scale/6.0.0?topic=fscc-specifying-maximum-number-files-that-can-be-created

m a x i m u m N u m b e r O f F i l e s = (t o t a l F i l e S y s t e m S p a c e) / (i n o d e S i z e + s u b b l o c k S i z e)

The sum of maximum number of inodes per fileset is not allowed to exceed this. Default inode size is 4096 bytes, and the subblock size is variable depending on the file system block size. Subblock size depends on file system block size:

64 KiB file system block size gives a 2 KiB subblock size
128 KiB file system block size gives a 4 KiB subblock size
256 KiB, 512 KiB, 1 MiB, 2 MiB, or 4 MiB file system block size gives 8 KiB subblock size
8 MiB or 16 MiB file system block size gives a 16 KiB subblock size

To test how many inodes we’re allowed to configure, we create a dummy file system on a sparse loopback device of various sizes:

# dd if=/dev/zero of=/root/diskimage.1PiB seek=1125899906842623 count=1 bs=1
# losetup /dev/loop1 /root/diskimage.1PiB
# echo loop1 generic > /var/mmfs/etc/nsddevices
# chmod 755 /var/mmfs/etc/nsddevices
# cat <<'EOF' > disk.desc
%nsd: device=/dev/loop1
EOF
# mmcrnsd -F disk.desc
# mmdelfs onePiBfs
# mmcrfs onePiBfs -F disk.desc -n 1 -i 512
Value '1000000000000000000' for option '--inode-limit' is out of range.  Valid \
 values are 1024 through 281474976710654.
Invalid argument
mmchfs: tschfileset failed.
mmchfs: Command failed. Examine previous error messages to determine cause.

# mmcrfs onePiBfs -F disk.desc -n 1 -i 1024
# mmchfs onePiBfs --inode-limit 1000000000000000000
Value '1000000000000000000' for option '--inode-limit' is out of range.  Valid \
 values are 1024 through 281474976710654.
Invalid argument
mmchfs: tschfileset failed.
mmchfs: Command failed. Examine previous error messages to determine cause.

# mmcrfs onePiBfs -F disk.desc -n 1 -i 4096
# mmchfs onePiBfs --inode-limit 1000000000000000000
Value '1000000000000000000' for option '--inode-limit' is out of range.  Valid \
 values are 1024 through 281474976710654.
Invalid argument
mmchfs: tschfileset failed.
mmchfs: Command failed. Examine previous error messages to determine cause.

Seems maximum number of inodes is independent on inode size.