mincache=direct option and RAID arrays

[mgais]

Hello,

I understood that mounting a filesystem with mincache=direct option would bypass the HP-UX buffers, and so it's recommended if the application uses already its own disk buffer.
But how does this relates to read/write caches that exist on RAID disk arrays?
Does the recommendation change its extent?

Thanks

[RAC_1 · Accepted solution]

This still hold true for raid disks.
The read/write buffer cache of raid disks still do what they do. In case you want to turn that off that would be from RAID setup. (Setting this off or very low would make RAID just crawl.)

The first one (setting of mincache=direct) if from OS perspective and later (cache setting on RAID) is on RAID.

[mgais]

Thank you.

So I should consider the RAID cache just like that one that is onboard any physical disk.
I deduct also that in cases where is appropriate to use the mincache=direct option, is NOT recommended to turn RAID cache off.

Is that correct?

[RAC_1]

You are correct.

Whether you set mincache=direct or not, never set RAID cache off. Why??
1. mincache=direct is specific to particular FS, while RAID cache is for all data that goes to RAID irrespective of which server it comes from or go to.
2. For apps that do buffer cahching at apps level (like oracle) you would want to avoid double buffering-at OS level and at apps level. So turning (or mimicking raw data access) you can avoid buffer caching at FS level.