VSAN-Troubleshooting-Reference-Manual

Diagnostics and Troubleshooting Reference Manual – Virtual SAN
Checking host memory requirements
The number of disk groups and the number of disks that can be supported in a disk
group is directly related to the amount of host memory available on an ESXi host in
the Virtual SAN Cluster. At a minimum, it is required that a host has at least 6GB of
memory. This will allow you to create a single disk groups, with one flash device and
one magnetic disk per host in hybrid configurations, or one flash cache device and
one flash capacity device in all-flash configurations. However, with only 6GB of
memory, there will be very little will be available for VMs to consume.
If the Virtual SAN configuration requires a host to contain the maximum number of
disks (7 magnetic disks x 5 disk groups in both all-flash and hybrid configurations),
then the host must contain 32GB of memory. These guidelines are the same for
Virtual SAN 5.5 and 6.0, as well as hybrid and all-flash configurations.
One final consideration is that the amount of host memory also impacts the number
of components that can be created on the Virtual SAN cluster. With 8GB of memory,
the maximum number of components supported is 750/host. With 32GB, one can
create the maximum number of components/host, which are 9,000. Components
will be covered in greater detail later in this manual.
Symptoms of host memory shortage
A symptom when there is a lack of host memory is that the following error is
displayed in the VMkernel log when you try to create a disk group. The operation
itself fails silently in the vSphere web client in vSphere 5.5. The ESXi host VMkernel
logs need to be examined to find the root cause of the problem:
2013-12-10T17:00:49.878Z cpu0:1000019952)WARNING: LSOMCommon:
LSOM_GlobalMemInit:1000: Unable to create LSOM slabs
2013-12-10T17:00:50.290Z cpu0:1000019952)WARNING: PLOG: PLOG_InitDevice:145:
Failed to initialize PLOG's memory: Admission check failed for memory resource
2013-12-10T17:00:50.296Z cpu0:1000019952)WARNING: PLOG: PLOGProbeDevice:3585:
Failed to init PLOG device
A similar error is thrown when trying to add new disks to a disk group:
2013-04-23T15:22:14.831Z cpu1:1000027564)WARNING: PLOG:
PLOGInitAndAnnounceMD:3780: Unable to allocate or get recovered
mpx.vmhba2:C0:T6:L0:2 state5257150e-b9d8-a627-4011-5a90cee6e862 failed Out of
memory
In 6.0, this behavior has been improved considerably and a warning is now
displayed in the vSphere web client if a shortage of memory resources is
encountered when trying to create a disk group.
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