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i'm just wondering how the memory in the vnxe3100 is being used.
the system comes with dual controller, 8GB per controller, but each controller has only 128MB read and 768MB write cache allocated (at least this is what unisphere says). is it ok? is there any way to increase those values? if not, what is the rest of the memory used for?
pkilian-chipmancorp.com
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Posted October 28th, 2011 08:00
I too would like to know this.
I bought my VNXe when they first came out so I only have 4 GB of memory per SP. The cost to upgrade to 8 GB is fairly high. My cache sits at 64 MB read and 384 MB write. To make matters even more confusing, in order to get decent performance from my NFS shares for ESXi VMs, I had to disable caching in the VM Advanced Attributes field. This seems counterintuitive.
Anyone from EMC care to comment?
Best Regards.
pkilian-chipmancorp.com
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Posted October 28th, 2011 09:00
tgraves,
Thanks for the response.
So in a VMware with NFS only environment, are you saying that no cache is used either for the RAID functions or the "front end" read system if that box is unchecked? I guess what I am asking is will the investment in the 8GB of memory per SP improve my ESXi performance.
Best Regards.
pdkilian,
The uncached option is specifically for writes. The front end does some write caching that helps many workloads, with one notable exception being VMware NFS. The RAID read/write caches are not affected by this setting.
Performance will generally improve by having more front end read cache. With more system memory, you will have a larger front end read cache.
i have to say that the performance is very poor even when compared to some low-cost iomega with 4 x 2 TB SATA drives.
in vnxe we are using 6 x 600 GB SAS drives (4+1 RAID5 + HS), disk array conected to ESXi as an iSCSI datastore. question is, does it make any sense to use SAS drives if the
maximum sequential 100% read (iometer in virtual machine) is around 50 MB/s? iomega via NFS can do over 100 MB/s in the same environment. random read+write goes down to 4-5MB/s.
network is definitely not a bottleneck, max throughout via iSCSI ports on the switch is never more than 400-500Mbps (gigE, 9000B jumbo frames)
tgraves1
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Posted October 28th, 2011 09:00
pc99096,
The write and read cache numbers reported are indicating the memory dedicated for RAID cache. The rest of the memory on the system is shared between "front end" read cache and the Unisphere management processes.
Also, memory needs to be reserved on the peer Storage Processor for failover purposes so the processes on the failed Storage Processor can run on the surviving Storage Processor.
pdkilian,
The latest version of VNXe will create new VMware NFS applications with caching disabled. This is the best practice, and will help performance significantly for VMware workloads. If you have VMware NFS applications that were created before the best practices fix, you should manually modify the application's settings to disable caching for best performance.