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Re: disk buffers

 
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Sam Miller_2
Occasional Advisor

disk buffers

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

Re: disk buffers

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...
A. Clay Stephenson
Acclaimed Contributor

Re: disk buffers

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.
If it ain't broke, I can fix that.
Sam Miller_2
Occasional Advisor

Re: disk buffers

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

Why else would they provide vxmemstat?
A. Clay Stephenson
Acclaimed Contributor

Re: disk buffers

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.
If it ain't broke, I can fix that.
James R. Ferguson
Acclaimed Contributor
Solution

Re: disk buffers

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...
Sam Miller_2
Occasional Advisor

Re: disk buffers

Thanks a lot!
Sam Miller_2
Occasional Advisor

Re: disk buffers

Your insight was very helpful.
Ted Buis
Honored Contributor

Re: disk buffers

HFS inodes are separate from VxFS inodes. Maybe that is what you were thinking.
Mom 6