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The Reserved Space Parameter
StorNext User’s Guide 328
• Yes - (Default) The MDC reserves enough disk space so that delayed
allocations can be converted to real allocations (even when the MDC
is restarted and the client is not). The MDC reserves a minimum of
about 4GB for each stripe group and up to 280MBs per actively
writing client for each stripe group.
•
No - More disk space is available for use, but buffer cache
performance is affected, and fragmentation may occur.
If the
MaxMBPerClientReserve parameter exists in the configuration file
and has a value of
0, ReservedSpace is set to No. Otherwise, ReservedSpace
defaults to
Yes.
Note: The amount of reserved space is usually less than 280MB per
client. Reserved space is calculated as 110% of the buffer cache
size of each particular client. For example, a client with a 64MB
buffer cache is allocated 70MBs of reserved space by the MDC.
If the client closes all files that are open for write, the 70MBs of
space is no longer accounted for. It is important to remember
that reserved space is per stripe group.
Note: In prior releases of StorNext,
MaxMBPerClientReserve defaulted
to 100MBs, and reserved space was the product of
MaxMBPerClientReserve multiplied by MaxConnections – 1. In
StorNext 3.0, the MDC tracks the actual amount of reserved
space that clients use but caps the value to about 280MBs per
client.
In addition, the MDC maintains a “minimum level” of
reserved space. As a result, in some cases, more reserved space
may be visible. Reserved space appears as allocated disk space
per data stripe group.
The minimum reserved space is enough to accommodate 15
clients or
MaxConnections – 1, whichever is lower. For example,
if a cluster has a
MaxConnections of 3, the reserved space total
can be under 1GB.