What is the best PE size for mirroring?

[Randy Hagedorn]

Hi,

I am building a new production Oracle server on HP-UX from scratch and want to get as much right as possible for disk configuration.

I am using 73GB Jamaica drives to contain our Oracle data and MirrorDisk/UX for redundancy. This system now has much more disk space than the old system, so to allow for future expansion, I've increased the PE size from 4MB to 64MB. By reading threads in the forum it seems that this shouldn't impact performance. Correct me if I'm wrong. I still have time to change it.

Question: With the increase in PE size, does this mean that I now have larger chunks of data at risk, thus increasing our vulnerability? I'm concerned!

Thanks,
Randy

[Sundar_7]

I would not go with 64 MB. Moderation is the key :-). Go with 8 MB.

Incase you need to created a distributed volume, this will have a HUGE impact on the performance.

[A. Clay Stephenson]

With one exception (and it really doesn't matter) PS size has no impact upon performance. The exception is extent-based stripping but here even the smallest allowed PE (1MB) is much too big to be a good stripe size -- so it doesn't matter. It's really just bookeeping in the kernel.

The size of the PE really has nothing to do with data vulnerabilty because the disk writes are much smaller. Now, if you are running without mirroring then you should be worrying about something important to data loss rather than a trivial concern as to the size of a PE as it relates to potential loss of data.

[Bill Hassell · Accepted solution]

The extent size is just a bookeeping task as Clay mentioned. NOTE: The extent size does not relate to database blocksizes. The actual task of writing/reading blocks does not relate to extents, rather, the extent map is used locate the desired block(s) by physical disk address and that's it. Now, 64Mb extents are designed for multi-terabyte filesystems so I would use 8meg or 16meg, giving you plenty of room for hundreds of Gb for future expansion.

[Randy Hagedorn]

By reading all replies, I have concluded that the increase in PE size will not adversely affect mirroring, due to smaller I/O's used by the disk devices.

Also, Bill's reply has me changing PE size to 16MB. If I need more disk space I will create another volume group to house the data, or maybe a SAN will come into play at that time.

Thanks all,
Randy