Considerations when evaluating current disk speed and NAS/SAN/NFS storage for the NetBackup master server.
NetBackup Master Disk I/O requirements
The NetBackup master server is a disk I/O sensitive application. Latencies in disk I/O will cause NetBackup to behave in an unpredictable manner. Average service times on disks housing anyportion of the NetBackup software, it's databases or the root drive, should be less than 20 msec. Additional disk layout recommendation can be found in the Best Practices for NetBackup Catalog layout
NetBackup master on a standard network share
Mounting any NetBackup master server components using a network share (ie NFS) is not Supported. Network shares do not contain strong enough file locking and IO ordering semantics which may result in data loss under normal operations.
NetBackup Master on SAN or NAS Storage
NetBackup uses SQL Anywhere as a component of the NetBackup operations, NetBackup can be mounted on a SAN or NAS Storage as long as these Sybase conditions are met and I/O average service times remain less than 20 msec. Additionally, the implementation of NAS/SAN storage should ensure reliability and resiliency in case of component failure.
STORAGE AREA NETWORKS (SANs) OR NETWORK ATTACHED STORAGE (NAS)
There are 2 main requirements for vendors of SAN/NAS hardware/software which determine whether or not SQL Anywhere will function properly:
1. The order of file writes is guaranteed. This means that if the server says write A, then write B, the SAN/NAS guarantees that A is written to the physical medium before B. Additionally, on Windows, Microsoft guarantees that a call to SetEndOfFile(...) followed by FlushFileBuffers(...) is sufficient to force the file metadata to the physical medium. We require those same semantics to be respected by a SAN/NAS.
2. When a write request is issued in this environment, the write has actually been completed to the physical medium (not buffered by the operating system or the driveâ€™s internal cache) when the SAN/NAS returns from the write call. This is generally true if point 1) above is enforced.
If the SAN/NAS does buffering, the order of the writes to the physical medium doesn't actually matter provided it absolutely guarantees that the file will always appear to have had all successfully completed writes applied to it even after a power loss. Typically, the "guarantee" is provided by a cache with battery backup.
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