File System size vs VSAM LDS allocation size
There is a difference between file system size (df command, zfsadm aggrinfo command output) vs VSAM LDS allocation size (LISTCAT command output).
Understanding Allocation size and file system size
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Log file
Records metadata changes. By default, its size is 1% of the disk size. However, it will never be smaller than 14 blocks and it will never be larger than 16,384 blocks (128 MB). -
Bitmap
Lists the blocks that are free on disk. The file size depends on the size of the aggregate. -
Aggregate File System List
Describes the file systems that are contained in the aggregate. For compatibility mode aggregates it is usually only one 8-KB block. -
8K Blocks
zFS File System allocation is based on 8K blocks, therefore z/OS zFS is able to allocate 6 blocks in 1 track, it means that 90 8 Blocks in 1 cylinder. -
Convert to track count to bytes
49152 Bytes in 1 track
6* 8192 < 56664 < 7 * 8192 <--- Unable to allocate 7 or more 8KBloks in 1 track.
So 15 tracks in 1 clylinder so allocate 90 8Kblocks per 1 cylinder.
We can convert from tracks or cylinders to bytes:
90 * 8 Kblocks /cilinder = 90 * 8192 bytes = 737280 Bytes = 720 KB / cilinder => 720KB / Clylinder
6 * 8 KBlocks / track = 6 * 8192 bytes = 49152 Bytes = 48 KB / track => 48KB / track
- cf) Normal dataset allocation
56664 Bytes in 1 track
56664 * 15 = 849960 = 830.0390625 = about 830KB / Cylinder
- File system size vs VSAM size
49152 : 56664 --> 56664 / 49152 = 1.15283203125, VSAM allocation size is about 15% greater than file system size.
References
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zfsadm fsinfo
https://www.ibm.com/docs/en/zos/2.4.0?topic=commands-zfsadm-fsinfo -
zfsadm aggrinfo
https://www.ibm.com/docs/en/zos/2.4.0?topic=scd-df-display-amount-free-space-in-file-system -
df
https://www.ibm.com/docs/en/zos/2.4.0?topic=scd-df-display-amount-free-space-in-file-system -
LISTCAT
https://www.ibm.com/docs/en/zos/2.4.0?topic=subcommands-listcat-command
HI-U-RBA is almost file system size, you can confirm HI-U-RBA / 8192 converting to 8K blocks.
https://www.ibm.com/docs/en/zos/2.4.0?topic=aggregates-dynamically-growing-compatibility-mode-aggregate