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Using diskpools (deviceclass=disk) or filepools (deviceclass=file) on a non-cached disk system is very slow, and therefore not usable.
Example (same setup in both cases):
TSM write to diskpoolon 8x Internal DISK = 8MB/s
AIX cp command on 8x Internal DISK = 300MB/s
The difference (as I understand it) is that the AIX cp command uses JFS2 read ahead and write behind mechanisms. TSM on the other hand waits for each 256KB write to complete before writing another 256KB block.
What we would like to see is that TSM would allow more 256KB blocks to be "in flight" (maybe using a parameter like "queuedepth" so it can be tuned) so that even on a non-cached disk system or wenn higher latencies occur on a cached disksystem, the disk can perform sequential IO and write multiple blocks at once and so improving throughput.
Idea priority | High |
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Due to processing by IBM, this request was reassigned to have the following updated attributes:
Brand - Servers and Systems Software
Product family - Storage
Product - Tivoli Storage Manager (TSM) Family
For recording keeping, the previous attributes were:
Brand - Tivoli
Product family - Storage
Product - Tivoli Storage Manager (TSM) Family
Thank you for submitting this request. In the case of disk with no write cache performance may be improved by turning off direct I/O via setting DIRECTIO NO in dsmserv.opt. This will allow the operating system to cache more data, resulting in better performance in that case. More information about this option is available in the TSM documentation: http://pic.dhe.ibm.com/infocenter/tsminfo/v7r1/index.jsp?topic=%2Fcom.ibm.itsm.perf.doc%2Ft_ptg_filesys_cache.html&resultof%3D%2522%2564%2569%2572%2565%2563%2574%2569%256f%2522%2520.