The J2_CFG_ASSIST ioctl operation returns the performance
statistics of a JFS2 file system.
The
J2_CFG_ASSIST ioctl operation returns a
cfg_assist structure,
as defined in the
/usr/include/sys/lvdd.h file. The structure
contains the following fields:
| Field |
Description |
| throughput |
Average throughput of disks under the file system
in MB/sec. For supported storage devices, throughput is obtained from
the device; otherwise runtime throughput of the file system is returned. |
| latency |
Average latency of all disks under the file
system in milliseconds. For supported storage devices, throughput
is obtained from the device; otherwise runtime latency of the file
system is returned. |
| flags |
Flags to be used. For a list of valid flags,
see the /usr/include/sys/lvdd.h file. |
| vg_max_transfer |
The maximum transfer size of the volume group
(VG), in KB. The vg_max_transfer field value is the maximum
amount of data that can be transferred in one I/O request to the disks
of the volume group. |
| write_atomicity |
Write atomicity in bytes. The write_atomicity field
value is the largest number of bytes that are not broken up when they
are written on aligned boundaries. |
The
J2_CFG_ASSIST ioctl operation returns the following
parameters only for supported storage devices; otherwise it returns
null values.
| Parameter |
Description |
| atomicWriteAlignment |
Required alignment for write atomicity in bytes. |
| ideal_sequential_read_size |
Ideal, sequential, read size of the disks under
the file system in KB. |
| ideal_sequential_write_size |
Ideal, sequential, write size of the disks under
the file system in KB. |
| ideal_random_read_size |
Ideal, random, read size of the disks under
the file system in KB. |
| ideal_random_write_size |
Ideal, random, write size of the disks under
the file system in KB. |
| stripsize |
The strip size of the disks under the file system
in KB. This is the amount of data that is contiguous on a single spindle
in the raid array. |
| stripesize |
The value of the Stripesize parameter
is in KB. (Stripesize = stripsize × number of spindles
in a RAID array - parity.) |
| parallelism |
The number of spindles that comprise the RAID
device that can be concurrently read from, or written to, in parallel. |
Return values
When you complete this operation, a value of 0 is returned. If
the operation fails, a value of -1 is returned and the
errno global
variable is set to one of the following values:
| Value |
Description |
| EFAULT |
Indicates that the copy of the parameter failed. |
| ENOMEM |
Indicates that the allocation of the memory
failed. |
| EAGAIN |
Indicates that the runtime statistics are unavailable
for any of the physical volumes under the file system. Try again after
more I/O has been issued to the file system. |