James Melin <[EMAIL PROTECTED]> wrote: >My VM guy here is saying that he read some place that having mini-disk >cache turned on for mini-disk volumes used by linux for system disk is a >good thing.
>My position has always been that Linux is caching what VM is caching and >it's a double fault. Since I'm not the VM guru (and neither is he really, >been doing VM here for just over a year) I don't have any traction in >getting this changed. As others have noted, "It depends" (and some of what I'm about to write also maps to what you and others have said; I'm not going to keep saying "as x said", for brevity). At the one end of the spectrum you have swap, which probably never (for varying values of "never") makes sense to cache. At the other end, you might have a heavily used R/O minidisk, which makes a fair amount of sense to cache *if the performance boost that this suggests is important*. Yes, stuff will get double-cached (triple-cached, if you count the controller) to some extent; you can't stop that. But you can control it a bit, by carefully tuning virtual machine sizes to minimize the amount of storage available for file cache, and then use minidisk cache. Assuming you have any handle on load on the machines, of course. VM minidisk cache is pretty smart; I'd be surprised if turning it on was generally a *bad* thing. Certainly turning it on for any frequently read data seems like it should be a good thing. We do recommend that the R/O minidisks that are part of the shared filesystem used by our product be cached, but that's a special case. And, of course, the bottom line is that VM can generate monitor data to let you really see whether it's doing any good. And Barton (or ASG) will be happy to sell you his product to analyze that data. ...phsiii ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
