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April 12th, 2011 11:00
LUN and RAID Group Utilization
My customer is using CX3-10c. The RAID Group utilization maximimzes to 96% and LUN utilization maximizes to 99-100%. At an average, they are around 50-60% utilized. Each disk is not utilized more than 40-50 % maximum. Is this an alarming situation? The LUN includes the Flare vault disks as well.
Should we rearrange the data by adding more disks to the RAID group and reallocating/striping data to new disks? If yes, is it going to bring in performance degradation for some time when the process is on?
I have three disks and can create a new RAID group and migrate one of the LUNs from this RAID Group i.e. migrate data from these LUNs to enw LUN for atleast one of the 100% utilized LUN. IS this a better option and will it bring the LUN utilization down for the LUNs on the existing RAID group?
RRR
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April 14th, 2011 07:00
At around 60 to 65% Little’s law kicks in and you’ll start to see a huge increase in response times. So when you see disk utilization of almost that value you should be hearing alarm bells to warn you of upcoming performance degradation. Remember that a disk can have 180 IOps (15000 RPM), but this will be 100% utilization and response times of individual IOs can be very large. I always try to stay at 2/3 of the max, everything above that can be noticable on critical servers as response times will go up exponentially.
natsidan
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April 14th, 2011 13:00
I would certainly move one of the luns away off on too another set of disks, one count for improved performance and another it is not best practice to have Luns with high throughput on the vault drives.