Re: Advice for IBM SSA disks

ralph.halter@pac.panmail.com wrote: > We are using Informix Mirroring because in questions of performance and > security there are no obvious advantages for AIX or Informix but it's more > transparent to our database monitoring and I get an e-mail via the alarm- > program when a chunk is down. > To achieve a well balanced distribution we have created several dbspaces per > disk and then distributed the tables across them. Now we check the > io-statistics per chunk from informix and the iostat command from AIX to find > bottlenecks and then use onunload/onload to move tables. For big tables we use > special dbspaces for fragmentation across multiple disks. But beware: there > are many factors to be considered when deciding on optimal fragmentation! > Again: we have decided on Informix fragmentation vs. AIX striping because it's > more transparent to us and to our db monitoring. > Hope this helps. > Cheers. > Ralph. > In article <6j6a60$d3d$1@news.xmission.com>, > Zeljan Silje <zeljan@laus.hr> wrote: > > my customers configuration is: > > - AIX4.2 > > - F50 machine (250 MB, 4x2.5GB + 4x4.5GB SSA disks, 1 processor) > > - Informix OnLine7.23 > > > > SSA disks (no raid) will hold the customers database. I have to decide > > how to spread database across SSA disks to provide balanced disk load > > and to provide mirroring. > > I think I have two options for balance disks load: AIX striping and > > Informix fragmentation. Does anyone have experience what shall be better > > on such configuration? If I use AIX striping what stripe size shall I > > use? > > If I decide on one of previous options, what mirroring is better: AIX > > mirroring or Informix? I agree with Ralph about the mirror issue, use Informix mirroring, it is easier to manage and will probably give a SLIGHT performance advantage. On the Fragmentation -vs- Striping issue I am going to disagree, in part. I believe that you should BOTH stripe across as many disks and controllers as possible (I use at least 10 drives but prefer 20-30 spread over 2 to 3 separate controllers) and then fragment your critical tables also. In this way you are unlikely to develop any REAL hot-spots. Striping should be with a 16K page size so that any single Informix BIGREAD comes from a single drive while readahead affects several drives. Also, when creating the 2GB virtual drive devices on the stripe set try to arrange things so that each successive virtual drive begins on a different disk and that the stripe is built such that successive drives are on different controllers, if possible. This will go a long way toward eliminating any hotspots. With this scheme only hitting the same 8 pages repeatedly could possible create a hostspot and Informix's BUFFER cache will prevent that from happening anyway. Your administration load of tracking I/Os to eliminate hotspots will dwindle SIGNIFICANTLY with this scheme. Art S. Kagel