Re: Compressed disk.. -- MIDRANGE-L

At 10:10 AM 8/5/99 -0700, you wrote:

Hi,

You're right, and this is how it works on V4R3 default as shipped.

When I discovered this, I bitched so loud that I actually got them to 
change it.  (In truth, I probably wasn't the only person bitching, but I 
might have been the loudest!)  In V4R4 the default is to overflow the User 
ASP.  You can then change it work like V4R3 with the new CHGASPA command.

I think that there's a PTF available for V4R3 to allow you to change the 
attribute.

Al


>Hello everyone...
>
>I've "discovered" something very interesting today. If you are using
>"compressed disk" on your AS/400 you probably want to read on...
>
>I have an S20 server. ASP2 in this server contains 10  8GB disks which have
>been configured as compressed disk.
>
>Yesterday I was experiencing problems with this S20 server. All disk I/O to
>ASP2 was suspended and there was an SRC code on the control panel that
>indicated all disk in ASP2 was full.
>
>What is interesting about this is that the WRKDSKSTS command indicated that
>the disk was only 58-65% full....
>
>How can this be?
>
>After a long conversation with IBM SupportLine I found out that the disk
>measurement algorithm in OS/400 makes some assumptions.
>
>One of these assumptions is that if you configure a disk as a "compressed
>disk" you will get at least a 2 to 1 compression on any data written to that
>disk. Therefore it assumes that a physical 8GB drive is now a virtual 16GB
>drive.
>
>This was probably more of a marketing decision that a technical one. I can
>hear the IBM marketing team now... "Lets show the disk as being twice as
>big!"  "The customer will think that they got a 16GB drive for the cost of
>an 8GB drive!!!"
>
>Well, no matter what the operating system reports, the disk is still an 8GB
>disk.
>
>Our problem was that we were sending lots of data to this ASP via NFS, that
>was already compressed. The disk IOP could not compress it any further,
>therefore the assumption that it could be compressed at least 2 to 1 didn't
>hold. We filled up our 10-8GB disk subsystem with this compressed data while
>the WRKDSKSTS command only reported that we were around 60% full...
>
>IBM is now aware of this problem. I'm waiting to hear from them if they are
>going to do something about it.
>
>In the mean time I have quite a challenge in how I'm going to manage my disk
>space.  Especially since I never really know how much disk is actually being
>used.
>
>
>Kenneth
>
>--
>********************************
>Kenneth E. Graap
>IBM Certified Specialist
>AS/400  Professional
>System  Administrator
>NW Natural - Information Services
>System Services
>Phone: 503 226 4211 X5537
>FAX:   603 849 0591
>keg@nwnatural.com
>********************************
>
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Al Barsa, Jr. - Account for Midrange-L
Barsa Consulting, LLC.  
400 > 390

Phone:          914-251-1234
Fax:            914-251-9406
http://www.barsaconsulting.com
http://www.taatool.com

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