maxphys
Parameter
- Description
-
Defines the maximum size of physical I/O requests. If a driver encounters a request larger than this size, the driver breaks the request into
maxphys
sized chunks. File systems can and do impose their own limit. - Data Type
-
Signed integer
- Default
-
131,072 (sun4v) or 57,344 (x86). The
sd
driver uses the value of 1,048,576 if the drive supports wide transfers. Thessd
driver uses 1,048,576 by default. - Range
-
stem-specific page size to
MAXINT
- Units
-
Bytes
- Dynamic?
-
Yes, but many file systems load this value into a per-mount point data structure when the file system is mounted. A number of drivers load the value at the time a device is attached to a driver-specific data structure.
- Validation
-
None
- When to Change
-
When doing I/O to and from raw devices in large chunks. Note that a DBMS doing OLTP operations issues large numbers of small I/Os. Changing
maxphys
does not result in any performance improvement in that case. - Commitment Level
-
Unstable