max i/o size

[Bipin Divakaran]

Oralce documention often talks about max i/o size of the operating system. What Oracle means by this is the largest chunk size that os can read/write in a single phycial i/o. Is there a command to find out this value?

[Vincenzo Restuccia]

Try iostat.

[Alan Riggs]

I haven't ever worked with this, so what follows is only a WAG.

The Filesystem limit to the size of an individual write is probably set by the ausize of the filesystem. At JFS version 3+ this is set at 32768 blocks. Block size, of course, can also be set. It defaults to 1024. I would think that any single write operation will be limited to space in a single allocation unit (for vxfs filesystems).

Alternatively, Oracle might be referring to the block size itself, or even the size of the physical extents defined for the VG in lvm.

Hmmm -- maybe this WAG isn't that helpful after all.

[Alan Riggs]

I forgot to mention -- for hfs filesystems you will absolutely be limited to a write size smaller than teh blocksize, since the superblock information is replicated at the beginning of each block.