Re: AIX - JFS2 Snapshots

_at_Mladen, it's not the case anymore. Most recent snapshot technologies do the so-called "redirect on write" (or "copy on first write") mechanism that limits the necessity of additional I/O, at the expense of higher file fragmentation. ACFS is an example easy to verify with `acfsutil info file`.

_at_Jeremy: beware that if you use TTS in conjunction with snapshots, you will end up by having inter-dependencies between 1 LUN and many Databases, so plan carefully your strategy, in particular naming conventions and snapshots and LUNs creation and deletion.

just my 2 cents...

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Ludovico



2016-02-23 5:10 GMT+01:00 Mladen Gogala <gogala.mladen_at_gmail.com>:



> 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 Guru’s,

>

>

>

> 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 Consultanthttp://mgogala.freehostia.com

>

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

>

>


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