For a CX4-240 the max write cache is 1.264GB. In most cases the best practice is to set the majority of memory to write cache. Most customers do either a 20% read and 80% write or a 10% read and 90% write. However, the real answer is it depends on your configuration.
Use Navisphere Analyzer to take a base line of where your performance is at now. Then try adding the free memory to your write cache and use Navisphere Analyzer to compare the results. You can start fine tuning it from there. If you are have a performance problem that is impacting your storage system then you need to open a support call.
Despite the fact that I hate hearing the answer "it depends" most of the time it is true. In this case Jen is right on the money. The answer to this question depends on what your array is being used for. That isn't always an easy thing to determine either. If these arrays were smaller and only hosted one application each it would be easy to say "I have a database that people run reports off of all day and has very little update activity". In a case like that you would clearly want to maximize your read cache. Extra write cache wouldn't do you much good.
As she pointed out, Navisphere Analyzer would be ideal for helping determine the workload and where you would get the most bang for your buck. If you don't have Navisphere Analyzer I would tend to err on the side of write cache. We generally maximize our write cache and allocate the rest to read. We have not yet run into a situation where this caused us performance problems, and we have a wide variety of apps running on every array (from file services to OLTP databases).
The other alternative if you don't have Analyzer (although it's usually worth the money anyway), is to talk to your EMC Account Team about a Professional Services engagement to analyze and optimize the configuration of the array. And before you ask... No, I'm not an EMC employee and I don't get commissions from PS *lol*
Table 9, CX4 Recommended Cache Settings, in EMC CLARiiON Best Practices for Performance and Availability, FLARE Revision 29 contains the latest recommendation for cache settings. This recommendation was developed by CSPEED. However, as previously mentioned, this is a 'works well under the great majority of workloads' allocation. A truely optimal allocation can be made using the previously mentioned 'deep-dive' performance analysis with Analyzer of workload historical data.
Jen_LeClair
111 Posts
1
February 11th, 2010 06:00
For a CX4-240 the max write cache is 1.264GB. In most cases the best practice is to set the majority of memory to write cache. Most customers do either a 20% read and 80% write or a 10% read and 90% write. However, the real answer is it depends on your configuration.
Use Navisphere Analyzer to take a base line of where your performance is at now. Then try adding the free memory to your write cache and use Navisphere Analyzer to compare the results. You can start fine tuning it from there. If you are have a performance problem that is impacting your storage system then you need to open a support call.
Allen Ward
4 Operator
•
2.1K Posts
1
February 11th, 2010 07:00
Despite the fact that I hate hearing the answer "it depends" most of the time it is true. In this case Jen is right on the money. The answer to this question depends on what your array is being used for. That isn't always an easy thing to determine either. If these arrays were smaller and only hosted one application each it would be easy to say "I have a database that people run reports off of all day and has very little update activity". In a case like that you would clearly want to maximize your read cache. Extra write cache wouldn't do you much good.
As she pointed out, Navisphere Analyzer would be ideal for helping determine the workload and where you would get the most bang for your buck. If you don't have Navisphere Analyzer I would tend to err on the side of write cache. We generally maximize our write cache and allocate the rest to read. We have not yet run into a situation where this caused us performance problems, and we have a wide variety of apps running on every array (from file services to OLTP databases).
The other alternative if you don't have Analyzer (although it's usually worth the money anyway), is to talk to your EMC Account Team about a Professional Services engagement to analyze and optimize the configuration of the array. And before you ask... No, I'm not an EMC employee and I don't get commissions from PS *lol*
jps00
2 Intern
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392 Posts
1
February 11th, 2010 07:00
norden1
9 Posts
0
February 12th, 2010 00:00
Thank you guys.
bye
kelleg
4 Operator
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4.5K Posts
0
February 12th, 2010 07:00
Was your question answered? If so, could you please mark the question as Answered and assign points to the answer that best fit your question?
glen