>We have serious performance issue for dsmfmt command. > >We are getting 45MB/sec write speed on AIX4.3.3 box connected to CX600 ATA >RAID5 4+1 disk group.But when we use dsmfmt it gives 9 to 16 MB/sec. Which >is very sluggish to format 16 TB storage for storage pools. > >Does anybody have information on how dsmfmt works? > > or how to speed up so that it will give better I/O on SAN storage?
Realize a few things... The 45MB/sec figure doesn't mean much without a lot of descriptive context. For example, a timing test using ordinary, buffered I/O is rather meaningless in that what's involved is principally the population of memory buffers rather than doing actual I/O. I have never seen any technical documentation on the workings of the dsmfmt command, but it may be doing synchronous I/O, which is necessarily slow. Things are slower still if the command is going back to check each block after writing for fidelity. File system block size, and file system fragmentation (in odd cases where the TSM "volume" is sharing space in a file system) are other factors. And then there is the RAID method: as has been discussed on the List, RAID 5 is particularly poor at sequential writing. (See http://www.pcguide.com/ref/hdd/perf/raid/levels/singleLevel5-c.html et al) Dsmfmt is the kind of utility not intended to be a high-performance thing, given that it's essentially intended to be used only for initialization, which is rather rare. You've received recommendations to use raw logical volumes because it eliminates the need for formatting: that approach is of particular value for disaster recovery. Richard Sims, http://people.bu.edu/rbs
