CompTIA Server+ (SK0-005)TroubleshootingHard
A server administrator notices that a newly deployed virtual machine (VM) on an ESXi host is exhibiting extremely poor disk performance, despite the underlying storage array being robust and other VMs on the same host performing normally. The VM's virtual disk is configured as 'thick provisioned, lazy zeroed'. Which of the following is the MOST likely cause of the poor performance?
- AThe initial zeroing process of the thick provisioned, lazy zeroed disk
- BNetwork I/O bottleneck on the ESXi host
- COutdated VMTools on the virtual machine
- DInsufficient CPU allocation for the VM
Show answer & explanationAnswer & explanation
Correct answer: A. The initial zeroing process of the thick provisioned, lazy zeroed disk
A 'thick provisioned, lazy zeroed' disk occupies its full allocated space immediately but does not zero out the blocks until they are written to for the first time. This 'on-demand zeroing' process, especially during initial writes or heavy I/O workloads, can introduce significant latency and consume disproportionate I/O resources, leading to poor disk performance for that specific VM until all blocks have been zeroed.
Why the other options are wrong
- B. Network I/O bottleneck would affect network-dependent operations, not primarily disk performance within the VM.
- C. Outdated VMTools can impact various aspects like network performance, mouse integration, or display, but typically not the raw disk I/O performance of a lazy zeroed disk in this specific manner.
- D. Insufficient CPU allocation would cause general processing slowness, but not specifically 'extremely poor disk performance' while other VMs on the same storage are fine.
Lazy Zeroed Thick Provisioning
A virtual disk provisioning type where the full disk space is allocated immediately, but blocks are zeroed out only when they are first written to by the guest OS.
- Consumes full space immediately.
- Zeroing on first write can cause performance spikes.
- Different from 'eager zeroed' (zeroed at creation) or 'thin provisioned' (grows as needed).
Memory trick: Lazy zeroing makes for slow starts.