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2 Intern
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174 Posts
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4039
April 22nd, 2013 03:00
Cache watermark level change cause any downtime?
Hi All,
We set the cache low/high watermark levels to 30%/50%. I read some blogs, bloggers said EMC recommendation is 60%/80%. I would like to change the watermark levels as per EMC recommendation. what will happen when i change the watermark levels on production hours.
Storage Model: EMC Celerra NX-4
Backend: Clariion AX-4 5F8
Flare: 2.23.50.5.711
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christopher_ime
2K Posts
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April 27th, 2013 16:00
I'll assume you are running Navisphere Manager 26 (with FLARE 23) and a newer version of Java. While running a recent version of Java is not an issue necessarily in itself; however, you most likely answered "Yes" to a Java prompt asking:
"Block potentially unsafe components from being run? (recommended)"
This appears when you access certain displays within Navisphere Manager such as "System Properties". Instinctively, people select "Yes", and I would agree it is recommended on webpages you aren't familiar with; however, that will unfortunately break functionality within the GUI as you had experienced. I will mention though if you managed your array with Unisphere (via domain management), you wouldn't get this prompt.
You can confirm you had (accidentally) answered: "Yes" if you only see the tabs:
1) General
2) Cache (NOTE: even though the Cache tab is displayed, several background Java scripts don't run)
On the other hand if you properly selected "No", then you'd see many more tabs:
1) General
2) Cache
3) Memory
4) Storage Access
5) Software
You have 2 solutions (*neither* requires disabling write cache or watermarks):
Solution #1
1) Close the GUI and clear both browser and java cache
2) When prompted, select "No" to the Java prompt
3) On the Cache tab modify in the following order:
a) Change the High Watermark first
NOTE: This is important as the GUI checks that Low watermark is < High watermark. If you were to try to change the Low watermark first, it would appear to not accept your input. However, in this case the new lw (60%) > old hw (50%).
b) Change the Low Watermark, then click OK
Solution #2
Modify via CLI:
1) naviseccli -h setcache -l 60 -h 80
NOTE: only need to run on one SP as it is a "mirrored" option
2) naviseccli -h getcache
3) naviseccli -h getcache
NOTE: (optional) verify that both SP's report the updated values
Vipin VK
2 Intern
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812 Posts
1
April 22nd, 2013 04:00
You can change the watermark settings even in production hours.
Anonymous User
457 Posts
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April 22nd, 2013 07:00
Hi,
You may also refer to below mentioned document and tread...
https://community.emc.com/docs/DOC-19387
https://community.emc.com/thread/109654?start=0&tstart=0
Regards,
Suman Pinnamaneni
Vipin VK
2 Intern
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812 Posts
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April 26th, 2013 00:00
There will be a small performance impact during the time when the cache (short time) is disabled.
Vipin VK
2 Intern
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812 Posts
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April 26th, 2013 00:00
Try disabling read and write cache and then changing the Water Mark values.
Dhakshinamoorthy
2 Intern
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174 Posts
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April 26th, 2013 00:00
Hi Suman and Vipin,
I cannot change the watermark levels.I changed the levels and click "Apply->OK" the screen stays long time.
christopher_ime
2K Posts
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April 27th, 2013 16:00
While you are reviewing "defaults", I had also noticed that the (Cache) Page Size is set to the non-default of 8KB. Could you provide more information on the environment and the (predominant) I/O size?
For instance, an example which may apply to your environment and the reason for the 16KB (Cache) Page Size is a Windows SQL environment where the volumes are (NTFS) formatted with a 64KB allocation size versus the default 4KB (NTFS) allocation unit size.
Otherwise, generally speaking 8KB is a good default in a "mixed" environment.
Dhakshinamoorthy
2 Intern
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174 Posts
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April 28th, 2013 11:00
Hi Christoper,
you are absolutely correct. I can change the watermark levels after selecting "No" when java prompt. Thanks for your help.
Dhakshinamoorthy
2 Intern
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174 Posts
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April 28th, 2013 11:00
Hi Chris,
Most of our environment uses SQL server database with NTFS partition with 4KB default allocation unit size and we have one Oracle Database Server. So that i selected "16KB" as a cache page size. Please suggest me is there any modification need.
I aware when we select 16KB cache page size, lot of wasted space appear and oracle win when we select 16KB.Please educate if i am wrong.
christopher_ime
2K Posts
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May 3rd, 2013 17:00
Good to hear that was the case.
christopher_ime
2K Posts
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May 3rd, 2013 18:00
I reread your original post and see that you own a unified platform (NX series). Assuming you are using the file portion of the array, in this case, you more-or-less fall under a "mixed" environment and is also one we suggest leaving at the default 8KB cache page size.
Dhakshinamoorthy
2 Intern
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174 Posts
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May 4th, 2013 03:00
Hi Christoper,
I have changed the cache page size to "8K".
christopher_ime
2K Posts
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May 4th, 2013 11:00
Yes, that is the preferred default in a unified platform (aside from an analysis via Analyzer of the predominant host I/O size as seen by the array). For your reference, I wanted to collect some of the passages that I like related to cache page size (available publicly at least). These are in recent copies of the Fundamentals and Best Practices for Performance and Availability Guides but related to this topic still pertain to your version of FLARE.