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Special Forums Hardware Filesystems, Disks and Memory Poor read performance on sun storedge a1000 Post 302302357 by TonyFullerMalv on Monday 30th of March 2009 07:00:29 PM
Old 03-30-2009
If a raid 10 made up of 12 disks is 6 disks in a striped volume mirrored against another volume of 6 disks in a striped volume, the the mirroring process (which has to write to both striped volumes) slows down writes compared with reading (which only has to read from one of the striped volumes), normally.

I think writing to /dev/zero is not a good idea, I would try writing to /dev/null instead.

Reading from /dev/random would be interesting to compare with reading from /dev/zero also?
 

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ndmpstat(1M)						  System Administration Commands					      ndmpstat(1M)

NAME
ndmpstat - show NDMP backup progress statistics SYNOPSIS
ndmpstat [tapes] [interval [count]] DESCRIPTION
The ndmpstat utility reports Network Data Management Protocol (NDMP) statistics, among which are NDMP worker threads, disk IO, tape IO, files operation, performance, and backup activity. ndmpstat reports the aggregate statistics for all tapes and disks. In order to obtain statistics for specific tape devices, the tape device name should be passed as argument to the utility. When invoked, ndmpstat begins its display with a one-line summary of the NDMP daemon activity since the NDMP service was invoked. Display Fields The fields in ndmpstat output are described as follows: wthr Report the number of worker threads in each of the four following states: r the number of worker threads running w the number of blocked worker threads that are waiting for resources such as I/O and paging b the number of backup operations currently running r the number of restore operations currently running file Report on usage of filesystem. rd the number of files being read wr the number of files being written disk Report the number of disk operations per interval. rd the number of disk blocks being read wr the number of disk blocks being written tape Report the number of tape operations per interval. There are slots for up to four tapes, labeled with a single number. The number indi- cates the name of the device under /dev/rmt. rd the number of tape blocks being read wr the number of tape blocks being written bytes Report the number of bytes transferred. This is the aggregate value of both tape and disk devices. The number is in kilobytes. rd the number of kilobytes being read wr the number of kilobytes being written perf Displays a rough estimate of performance of the backup/restore operation in megabytes per second. bk backup performance rs restore performance prcnt Display the comparative usage of resources, in percent. dsk disk I/O time tpe tape I/O time otr other time (memory or idle) See EXAMPLES. OPERANDS
The following operands are supported: count Specifies the number of times that the statistics display is repeated. tape Specifies which tapes are to be given priority in the output. A command line is limited to a maximum of four tape devices. A common tape name is /dev/rmt/n, where n is an integer. interval Specifies the number of seconds over which ndmpstat summarizes activity. The specified interval remains in effect till the com- mand is terminated. EXAMPLES
Example 1 Using ndmpstat The following command displays a summary of NDMP daemon activity at five-second intervals. example% ndmpstat 5 wthr file disk tape bytes perf prcnt r w b r rd wr rd wr rd wr rd wr bk rs dsk tpe otr 1 0 3 6 50 9 1250 0 32544 4455 42335 3234 5 4 20 40 40 1 0 0 1 1 0 128 0 0 128 64 64 1 0 0 80 20 1 0 0 1 2 0 128 0 0 0 64 0 1 0 80 0 20 1 0 0 1 1 0 128 0 0 0 64 0 1 0 80 0 20 1 0 0 1 3 0 128 0 0 0 64 0 0 0 80 0 20 1 0 0 1 1 0 128 0 0 128 64 64 1 0 0 80 20 ^C example% ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWndmpu | +-----------------------------+-----------------------------+ |Interface Stability |See below | +-----------------------------+-----------------------------+ Invocation is evolving. Human readable output is unstable. SEE ALSO
iostat(1M), mpstat(1M), ndmpd(1M), ndmpadm(1M), attributes(5) NOTES
Performance numbers are not accurate and are rounded up at the MB/sec. boundary. SunOS 5.11 21 Jun 2007 ndmpstat(1M)
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