bigdisk> snap reserve Current snapshot reserve is 10% or 18976480 k-bytes.
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bigdisk> snap list working...................................................... %/used %/total date name
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7% ( 4%) 3% ( 1%) Feb 17 00:01 nightly.1
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bigdisk> df Filesystem kbytes used avail capacity Mounted on / 170788336 71454936 99333400 42% / /.snapshot 18976480 5180276 13796204 27% /.snapshot
The question is:
Snap list seems to be saying that snapshots consume 7% of a total 10% in my snapshot reserve, for a total of 70% of reserve consumed.
Yet "df" says that I'm only consuming 27% of the snapshot reserve.
What gives?
What gives is that the first column (%/used) measures the space consumed by snapshots as a percentage of space USED, rather than as a percentage of the TOTAL available.
Thus, the first column is a good estimate of what snapshots would be consuming if the filesystem were full.
The second column (%/total) measures the space consumed by snapshots as a percentage of the TOTAL space in the filesystem. Since your filesystem is about half full, you would expect this to be about half of the first column.
In summary, your first reaction was correct. To safely handle another nightly snapshot, you may need to increase the snapshot reserve just a bit. Since the FS is only half full, you have plenty of spare reserve at the moment, but if the FS were full, you might not.
It's possible, depending on the nature of the data you are storing, that the rate of change won't increase as you store more data. In this case, the %/total column would be a better reflection of utilization patterns even when the FS is full. On the other hand, if you are adding additional users over time, and you expect them to behave about like the existing ones, then %/used is probably a safer measure.
Dave