topic Re: disk buffers in Operating System - HP-UX

disk buffers

Sam Miller_2 — Wed, 09 Nov 2005 12:01:12 GMT

I was wondering if disk buffer is being user for veritas filesystems or it it is only applicable to ufs filesystems. ANy help?

Re: disk buffers

James R. Ferguson — Wed, 09 Nov 2005 12:09:40 GMT

Hi Sam:

I assume that you mean "buffer cache" when you say "disk buffer". Yes, the buffer cache is used by JFS (VxFS) as well as HFS filesystems, unless specifically altered on JFS filesystems using mount options like 'mincache=direct' and/or 'convosync=direct'.

Regards!

...JRF...

Re: disk buffers

A. Clay Stephenson — Wed, 09 Nov 2005 12:18:32 GMT

In HP-UX speak, ufs filesystems are actually hfs and are used only rarely these days except as boot filesystems. In any event, both hfs and vxfs filesystems utilize the buffer cache. If by "disk buffer" you mean that on a physical drive or an array then that cache is completely invisible to the OS.

Re: disk buffers

Sam Miller_2 — Wed, 09 Nov 2005 13:11:33 GMT

thanks for the imput. I thought veritas has its own cache, separate for the buffer cache.

Why else would they provide vxmemstat?

Re: disk buffers

A. Clay Stephenson — Wed, 09 Nov 2005 13:19:56 GMT

I suspect so that a cross-platform command is available. You should realize that the disk caching occurs even below the filesystem abstraction layer --- indeed, that is the distinction of block and character disk device nodes. There are ioctl()'s that will alter the behavior of normally buffered i/o to unbuffered i/o -- that is how the vxfs VX_DIRECT option is implemented.

Re: disk buffers

James R. Ferguson — Wed, 09 Nov 2005 14:08:35 GMT

Hi (again) Sam:

With JFS 3.5 a separate Metadata Buffer Cache is introduced for file system structural information. Prior to 3.5 this was part of the standard buffer cache.

Regards!

...JRF...

Re: disk buffers

Sam Miller_2 — Wed, 09 Nov 2005 15:52:07 GMT

Thanks a lot!

Re: disk buffers

Sam Miller_2 — Wed, 09 Nov 2005 15:54:30 GMT

Your insight was very helpful.

Re: disk buffers

Ted Buis — Thu, 10 Nov 2005 10:39:29 GMT

HFS inodes are separate from VxFS inodes. Maybe that is what you were thinking.