Re: (no subject)

From: Tim Gorman <tim_at_sagelogix.com>
Date: Wed, 30 Jun 2004 11:04:06 -0600
Message-ID: <BD084EA6.177DA%tim@sagelogix.com>

Prem,

Obviously, you can choose any file size from 0 to 16tb, but I imagine that what you are seeking is a reason to choose any one size over another?

Might I suggest that the speed at which your tape subsystem can backup and restore a file determine the most desirable maximum size?

Most backup mechanisms devote only one process to each datafile during backup and during restore. Parallelism can be achieved by opening multiple such processes on multiple datafiles and multiple tape drives, but the essential atomic unit of backup/restore is the datafile.

So look at the size of the datafile as determining the fastest possible backup/restore operation.

If you make your database out of four 1tb files, then the fastest possible backup/restore operation will be however long it takes to backup/restore 1tb. Even if you have only one 1tb file, then the fastest full database backup/restore operation would still be constrained by how long it takes to read/write that 1tb file.

With that in mind, you should conclude that it makes a whole lot more sense to construct that tablespace of 1tb out of 128 8gb datafiles, instead of on= e
1tb datafile. Both sizes (1tb and 8gb) are feasible from the file-system/O= S
perspective, but 8gb has the advantage of enabling more parallelism during backup/restore or file-copy operations.

So, to determine whether 2gb, 4gb, 8gb, 16gb, or 1tb is the best file size, I suggest that you conduct some testing on backing up and then restoring files of those sizes, and then choose according to the most desirable ratio of timing to throughput.

Or, just do what I do and arbitrarily choose "8gb" as the largest datafile size... :-)

Just my $0.02...

Hope this helps!

-Tim

on 6/30/04 3:19 AM, Prem Khanna J at premj_at_rediffmail.com wrote:

> Thanks All.=20
> we use JFS2 (on AIX5.2L).
> AIX docs say that it supports files as large as 16TB.
> that's too large.

>=20

> Raj>We have used 16GB at times ... but we use sushi files
> (raw not cooked)

>=20

> Raj,Hope u were in Japan for a while ;)

>=20

> from your experience, any suggestions for JFS2 ??
> 2GB or 4GB or 8GB .... ?!!!

>=20

> Thanks and Regards,
> Prem.

>=20

> =A0

>=20


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Received on Wed Jun 30 2004 - 12:01:24 CDT