You could consider using Navisphere Analyzer ! Lots of details in there If you look up detaisl for a specific LUN, it's for that LUN only. You'll need to add up all details for all LUN's to get a total. If you use Analyzer, you'll get much more ways to get stats.
But.... out of curiousity: why do you call your Clariion a SAN ? The SAN is the network the Clariion is conencted to, so the FC switches ! The Clariion is called Storage Array and it's connected to the SAN with a few fiber patch cables .
Thanks, I am using Navisphere Analyzer to get the Forced Flushes/S rate. So I guess that if I see 50 FF/sec on one Lun and another 40 FF/Sec on another LUN, then, assuming these are the only 2 LUNs, that would equal 90 FF/sec overall on the whole storage array (Thanks for clarifying between Storage array and SAN - makes sense!).
A better way to look at force flushing for the whole array is %Dirty Pages. Force Flushing begins when the Write Cache% Dirty Pages exceeds the High Watermark. If your watermarks are set to 60/80 (the normal default), when % Dirty Pages exceeds 80%, the cache will start to force flush - typically on the LUN(s) causing the cache to get filled up, but also other LUNs that are close to 80% full.
If %Dirty Pages gets to 99% full, then the cache is completely full and can accept no more Writes - then the whole write cache will start to force flush - you want to avoid this if possible as it will slow down everyone using the array.
Check the On-Line Help - there is a section specifically for Analyzer that has a lot of good information.
this is exactly what I was looking for. Thanks for your help. I actually have a PDF document on Navi Analyzer, but I'll check on-line help for more info.
I'm glad you got your answer and I noticed you marked your question as "answered". If there's a post that helped you in particular or partial, could you please mark these post as such ?
Right click on the array go to properties. Click on the Cache tab. At the bottom you will see Percent dirty pages. if you see this hitting 99 percent you are getting forced flushing. All the other ways are definately better than this because you get the historical data
I was looking at some navi logs over a 5 day period and noticed having consistent high watermarks...mostly in the upper 70s. There were a few 90s and one was at 99. My watermark is currently using the default settings of 80-60 and I was wondering if I should change it to 60-40 to see if I can get some performance on my hosts.
If I understood correctly, if the dirty pages hit 99%, that write cache is disabled and that the SP will perform a 'forced' flush until it hits the low watermark. And i know if it hits above 80 that it will also performs a forced flush. Let's say it was at 81%...does that mean that cache is also disabled until it hits 60 or does that only pertain to when dirty pages hits 99% because there's no room?
At what point, after looking at the logs, dictates whether I should drop my watermark settings? For example, if I'm seeing consistent dirty pages at the high 70% levels, and if I'm considering dropping the watermark to 60-40, wouldn't I be seeing more forced flushes? And isn't several forced flushes bad?
I wouldn't lower the low and high watermarks. If the HW is set to 60 and cache usage is over 60%, forced flushing will begin sooner and this might have a more serious performance impact. I'd suggest to experiment to set the LW and HW to 90/70. This way the cache is used more effectively. You will see more forced flushes though, but that flushing is over more quickly as well, since the LW is higher as well
I have seen people experimenting with values of 50/70, but that was in specific database environments. I know there are threads on the forums about this.
When the amount of Dirty Pages exceeds the High Watermark, the cache will start to force flush the pages to the disks and continue until the Low Watermark is hit. During this time the cache is still open. It's only when you hit 99% Dirty Pages that the Write cache shuts off.
If you're only seeing one or two points hitting 99%, you're probably OK with the current settings. Normally you want to see Dirty Pages oscillate between 60% and 80%.
You can make changes to the Watermarks on the fly, if you do decide to change the settings, change the low mark first - try to keep at least 20 points between the Low and High.
A better solution is to look at the amount of Write cache you have allocated - generally you should assign a low amount to Read cache and the rest to Write cache. You can usually get away with from 50-100MB of Read cache depending on your environment. The Best Practice guides have some recommendations for cache settings.
EMC CLARiiON Storage System Fundamentals for Performance and Availability
skong
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May 10th, 2009 04:00
Thanks again!
SKT2
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May 10th, 2009 07:00
RRR
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May 11th, 2009 03:00
But.... out of curiousity: why do you call your Clariion a SAN ? The SAN is the network the Clariion is conencted to, so the FC switches ! The Clariion is called Storage Array and it's connected to the SAN with a few fiber patch cables
skong
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May 11th, 2009 06:00
kelleg
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May 11th, 2009 07:00
If %Dirty Pages gets to 99% full, then the cache is completely full and can accept no more Writes - then the whole write cache will start to force flush - you want to avoid this if possible as it will slow down everyone using the array.
Check the On-Line Help - there is a section specifically for Analyzer that has a lot of good information.
glen
skong
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May 11th, 2009 10:00
RRR
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May 12th, 2009 01:00
I'm glad you got your answer and I noticed you marked your question as "answered". If there's a post that helped you in particular or partial, could you please mark these post as such ?
mpalumbo1
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May 12th, 2009 06:00
Right click on the array go to properties. Click on the Cache tab. At the bottom you will see Percent dirty pages. if you see this hitting 99 percent you are getting forced flushing. All the other ways are definately better than this because you get the historical data
Hope this helps.
Mike
odurasler
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February 12th, 2010 17:00
All,
I was looking at some navi logs over a 5 day period and noticed having consistent high watermarks...mostly in the upper 70s. There were a few 90s and one was at 99. My watermark is currently using the default settings of 80-60 and I was wondering if I should change it to 60-40 to see if I can get some performance on my hosts.
If I understood correctly, if the dirty pages hit 99%, that write cache is disabled and that the SP will perform a 'forced' flush until it hits the low watermark. And i know if it hits above 80 that it will also performs a forced flush. Let's say it was at 81%...does that mean that cache is also disabled until it hits 60 or does that only pertain to when dirty pages hits 99% because there's no room?
At what point, after looking at the logs, dictates whether I should drop my watermark settings? For example, if I'm seeing consistent dirty pages at the high 70% levels, and if I'm considering dropping the watermark to 60-40, wouldn't I be seeing more forced flushes? And isn't several forced flushes bad?
RRR
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5.7K Posts
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February 13th, 2010 03:00
I wouldn't lower the low and high watermarks. If the HW is set to 60 and cache usage is over 60%, forced flushing will begin sooner and this might have a more serious performance impact. I'd suggest to experiment to set the LW and HW to 90/70. This way the cache is used more effectively. You will see more forced flushes though, but that flushing is over more quickly as well, since the LW is higher as well
I have seen people experimenting with values of 50/70, but that was in specific database environments. I know there are threads on the forums about this.
Suggestions anyone ?
odurasler
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February 13th, 2010 08:00
good point.
i would assume that making changes to the watermark settings is non-disruptive and can be done on a fly?
kelleg
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February 15th, 2010 08:00
When the amount of Dirty Pages exceeds the High Watermark, the cache will start to force flush the pages to the disks and continue until the Low Watermark is hit. During this time the cache is still open. It's only when you hit 99% Dirty Pages that the Write cache shuts off.
If you're only seeing one or two points hitting 99%, you're probably OK with the current settings. Normally you want to see Dirty Pages oscillate between 60% and 80%.
You can make changes to the Watermarks on the fly, if you do decide to change the settings, change the low mark first - try to keep at least 20 points between the Low and High.
A better solution is to look at the amount of Write cache you have allocated - generally you should assign a low amount to Read cache and the rest to Write cache. You can usually get away with from 50-100MB of Read cache depending on your environment. The Best Practice guides have some recommendations for cache settings.
EMC CLARiiON Storage System Fundamentals for Performance and Availability
http://powerlink.emc.com/km/live1/en_US/Offering_Technical/White_Paper/H1049_emc_clariion_fibre_channel_storage_fundamentals_ldv.pdf
EMC CLARiiON Performance and Availability Release 29.0 Firmware Update Applied Best Practices.pdf
http://powerlink.emc.com/km/live1/en_US/Offering_Technical/White_Paper/h5773-clariion-best-practices-performance-availability-wp.pdf
glen