VNX/VNXe Family: General Storage Performance Terminology

Summary: VNX/VNXe Family: General Storage Performance Terminology

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Instructions

  • Throughput: A measurement of data being exchanged, in the number of Inputs and Outputs per Second (IOPS)
  • Bandwidth: A measure of the data being Moved, in MB/s
  • Response time: This measures the time interval between the issue and the fulfillment of the request. This is a calculated value using IOPS and Queue Length - under 20 ms is considered good. One caution, with low IOPS (under 100) and low Queue Length (under 2-3), Response Times can be artificially high.
  • Utilization: A measure of how busy is the SP, the LUNs, the Disks, or RAID Groups are. This is not an indication of a problem, unless SP usage is >60%. This leads to performance problems if one SP fails.
  • Queue Length: A measure of how many IO s are starting to back up in the queue under 10 is a good number.
  • Dirty Pages: A measure of the number of writes to a LUN that are in the write cache (and not yet written to disk).
  •  Force Flushing: This occurs when the write cache is full and can t take any more IOs until it flushes (de-stages) the writes to the disks. This causes response times and queue lengths to go up and affect other LUNs on the array. Try to avoid this.  See KB Article 332999
  • Random: I/O Which is addressed to regions on the LUN which are distant from each other.
  • Sequential: I/O to regions on the LUN which are adjacent.
  • Average Seek Distance: A measure of the amount of distance the disk head move, expressed in GB. The higher the number, the greater the head movement. This might indicate a lot of random IO bad for response times. High Seek distances, combined with heavy I/O, are an indication of drive contention.
  • Skew: This is the difference in I/O levels between the busiest and the most idle blocks on a LUN. Database tables would have a high skew, whereas a full backup would have minimal skew.
     

Affected Products

VNX/VNXe

Products

VNX1 Series, VNX2 Series, VNX/VNXe
Article Properties
Article Number: 000022618
Article Type: How To
Last Modified: 13 May 2025
Version:  7
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