Issue:
VNX Block-only arrays ship by design with zero read and write cache values.
VNX Unified/File system installations set read and write cache values contrary to "best practices"
Cause:
For VNX File/Unified systems, the installation of the File component [as a File re-install or as a Block-to-Unified upgrade], at File OE versions 7.0.12.0/7.0.13.0/7.0.14.0, sets the Read cache values on the SPs to a flat value of 512 MB/SP on all Unified models. However, this behavior contradicts theen standard Best Practice values for VNX arrays. Users need to be aware that they may need to manually set the Read cache value back to the desired settings after a File install.
With VNX File OE version 7.0.35.3 and later, the Block-to-Unified upgrade, or a File re-install, will not change any array cache values, if already set. However, where array cache values have not already been set, a File system installation will appropriately set the array cache values to the recommended settings outlined in the Table below. Basically, Read cache values will be set at 10% of available cache (with a Read minimum of 256 MB, and a Read maximum of 1024 MB), and the
remainder of cache assigned to Write cache as described in the table below.
Max. Cache/SP (GB) 4 8 12 18 24/48*
Allocate 10% of available cache to read (Read cache is set per SP, with a minimum of 256 MB, except for the VNX5100, and a max of 1024 MB), and the rest to write (Write cache is set per array). Please note that certain Array features, such as FAST VP and Compression, will reduce the overall memory available for Read and Write cache, hence the minimum 256 MB Read cache reference. Setting read to 10% (with min and max) would lead to the following:
VNX Block-only arrays ship by design with zero read and write cache values.
VNX Unified/File system installations set read and write cache values contrary to "best practices"
Cause:
This article offers basic guidance for suggested cache settings on VNX Block systems at installation time. VNX Block-only systems ship from the factory without any Read/Write cache values assigned, and with cache totally disabled on both storage processor (SPs). The Block-only versions of the VNX Installation Guides instructs users to setup the initial Read/Write cache settings for the array during the installation process. In addition, users should understand that the initial cache settings may need to be changed once normal and proper system operation/performance has been determined.
For VNX File/Unified systems, the installation of the File component [as a File re-install or as a Block-to-Unified upgrade], at File OE versions 7.0.12.0/7.0.13.0/7.0.14.0, sets the Read cache values on the SPs to a flat value of 512 MB/SP on all Unified models. However, this behavior contradicts theen standard Best Practice values for VNX arrays. Users need to be aware that they may need to manually set the Read cache value back to the desired settings after a File install.
With VNX File OE version 7.0.35.3 and later, the Block-to-Unified upgrade, or a File re-install, will not change any array cache values, if already set. However, where array cache values have not already been set, a File system installation will appropriately set the array cache values to the recommended settings outlined in the Table below. Basically, Read cache values will be set at 10% of available cache (with a Read minimum of 256 MB, and a Read maximum of 1024 MB), and the
remainder of cache assigned to Write cache as described in the table below.
Resolution:
The following recommended default cache settings (by model) should be considered as a starting point, and are valid for a Block-only or Unified installation.
Refer to the VNX Best Practices Guide for guidance on how to adjust these settings for your particular workload. Refer to knowledge base 78781 for examples
of how to change Read and Write cache values using Unisphere.
Refer to the VNX Best Practices Guide for guidance on how to adjust these settings for your particular workload. Refer to knowledge base 78781 for examples
of how to change Read and Write cache values using Unisphere.
Per Storage
Processor Memory VNX5100 VNX5300 VNX5500 VNX5700 VNX7500
Max. Cache/SP (GB) 4 8 12 18 24/48*
Max. Write Cache (MB)
Release 32 without enablers 950 3997 6488 9706 13450/-
Max. Write Cache (MB)
Release 32 and data services** 650 2782 4738 6581 10600/16600
Release 32 and data services** 650 2782 4738 6581 10600/16600
Allocate 10% of available cache to read (Read cache is set per SP, with a minimum of 256 MB, except for the VNX5100, and a max of 1024 MB), and the rest to write (Write cache is set per array). Please note that certain Array features, such as FAST VP and Compression, will reduce the overall memory available for Read and Write cache, hence the minimum 256 MB Read cache reference. Setting read to 10% (with min and max) would lead to the following:
- VNX5100 - Read 100 MB [Block-only system]
- VNX5300 - Read 400 MB [Block or Unified/File]
- VNX5500 - Read 700 MB [Block or Unified/File]
- VNX5700 - Read 1024 MB [Block or Unified/File]
- VNX7500 - Read 1024 MB [Block or Unified/File]
