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General Operating Guidelines and Limitations
StorNext User’s Guide 348
All As of SNFS 2.7, a change was made to the way that the Reserved Extents
performance feature affects free space reporting. In the previous release,
SNFS would reserve a certain amount of disk space which would cause
applications to receive an
out of space error before the disk capacity reached
100%.
In the current release, this reserved space is treated as allocated space. This
allows applications to perform allocations until the file system is nearly full.
NOTE: Due to allocation rounding, applications may still receive a premature
out of space error, but only when there are just a few megabytes of space
remaining. In the worst case, the error will be returned when the reported
remaining space is:
(InodeExpandMax * #-of-data-stripe-groups)
One side effect of this change is that after creating a new file system,
df will
show that space has been used, even though no user data has been allocated.
The amount of reserved space varies according to client use but does not go
below a “floor” of a few gigabytes per data stripe group. The amount of
reserved space at any time can be seen using the
cvadmin command, selecting
the file system, and using show long.
While not recommended, the Reserved Extents feature can be disabled by
applying the following setting to the Globals section of the FSM
configuration file:
ReservedSpace No
This will cause the file system to not reserve space for buffered I/O, thereby
reducing buffer cache performance and possibly causing severe
fragmentation.
For more information, see The Reserved Space Parameter
on page 327 and
the
cvfs_config(4) man page.
Operating System /
Affected Component Description