This article discusses an issue resolved in ESXi 5.5 Patch 08 and ESXi 6.0 Patch 03.
If the error "VDDK error: 1 (Unknown error)." occurs with an ESXi host running a version more recent than ESXi 5.5 Patch 08 or ESXi 6.0 Patch 03, it is advisable to engage with both VMware support and Veeam support.
VDDK error: 1 (Unknown error).
This issue occurs when too many performance counters are being registered on the ESXi hosts vpxa process causing the process to run out of memory.
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