The Reserved Space Parameter
•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.
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.
•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: 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.
StorNext User’s Guide | 328 |
