Re: AIX - JFS2 Snapshots

From: Mladen Gogala <>
Date: Mon, 22 Feb 2016 23:10:19 -0500
Message-ID: <>

Jeremy, snapshot is just a set of pointers. Using snapshot will just move the CPU usage from your DB server to your disk array, if you are using SAN snapshot. Snapshot is NOT a copy. It's a set pointers which is kept accurate to point in time by combining the pointers with COW. There are two possibilities:
  1. You are doing SAN snapshots and what is being snapped is a LUN. In this case, reading the snapshot will use CPU of the SAN and, because of optimized algorithms, will not have a profound impact on your system.
  2. You are doing file system snapshots, which are done using the COW method (copy-on-write). That is as bad as it can get. Each snapshot will triple your IO rate. The explanation is simple: to write the new data to your original location you must: 1) read the old data 2) write the old data to the new location and 3) write the new data. That means that for every write, you need to do 3 IO operations. If this is on your DB system, I wish you a good luck.

A word of advice: test your ideas before putting them in practice. People often confuse snapshots for copies. Let me repeat: snapshots are NOT copies.

On 2/19/2016 11:10 AM, Sheehan, Jeremy wrote:
> Hello Guruís,
> Has anyone used JFS2 Snapshots with Oracle in any capacity? We have
> an old process that uses a filesystem copy in combination with
> transportable tablespaces to move datafiles from one db to another.
> We are looking to eliminate the filesystem copy and replace it with
> JFS2 snapshots. This is being done to eliminate CPU resources and
> speed up the process (about an hour per tablespace grouping x 3/day x
> 3 tablespaces).
> If you have used something in a similar manner, any gotchas to keep an
> eye out for? Any advice? Please let me know.
> Thanks in advance!
> Jeremy

Mladen Gogala
Oracle Consultant

DISCLAIMER: I am solely responsible for any opinion expressed in this email

Received on Tue Feb 23 2016 - 05:10:19 CET

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