Esxi | Ramdisk Full Work
When an ESXi ramdisk becomes full, it often brings critical host operations to a standstill. Because ESXi runs largely in-memory for speed, it uses ramdisks—filesystems mapped directly into the system's RAM—to store temporary data, logs, and configuration state. When these small, predefined partitions hit 100% capacity, you may see errors like "The ramdisk 'root' is full," host unresponsiveness, or an inability to perform vMotions or enter maintenance mode. Symptoms of a Full ESXi Ramdisk vCenter Alerts: Direct warnings stating "The ramdisk 'root' (or 'var', 'tmp', 'opt') is full". vMotion Failures: The hostd service cannot create necessary journal headers, blocking VM migrations. Missing Logs: Systems logs in /var/log/ stop updating because there is no space to write new data. Unresponsive Host: Configuration changes or administrative commands (like esxcli software vib list ) fail with "No such file or directory" errors. Immediate Identification and Diagnostics To pinpoint which ramdisk is causing the issue, log in to the ESXi host via SSH and run: vdf -h This command displays the size, used space, and available space for all ramdisks. If any show 100% Use% , they must be investigated immediately. Common Culprits to Check ESXi host RAM disk is full - Broadcom support portal
In the quiet hum of the server room, the is often a silent workhorse, but a "ramdisk full" error can turn a routine day into a high-stakes troubleshooting mission. This is the story of how a small, volatile partition can bring even the most robust virtualization environment to its knees. The Warning Sign The incident usually begins with a cryptic alert in the vSphere Client "The ramdisk 'root' is full." . Suddenly, critical operations start to fail: fails to initiate, trapped by a "general system error". Host Management becomes sluggish or completely unresponsive as the service struggles to write new entries. stop updating, leaving administrators blind to what is actually happening under the hood. The Investigation Armed with an SSH session , the administrator dives into the command line. A quick command confirms the suspicion: one of the ramdisks—often 100% capacity The culprit is usually one of three usual suspects: Solve Ramdisk Full Error Issue Post Upgrading to ESXi 6.5
This feature explains what the ESXi ramdisk is, why it fills up, the operational impact, diagnostic commands, and permanent remediation strategies.
Feature: Understanding and Resolving the "Ramdisk Full" Condition on VMware ESXi 1. Overview: What is the ESXi Ramdisk? VMware ESXi is a purpose-built bare-metal hypervisor. Unlike traditional operating systems, it has a minimalist design. A critical component of its runtime environment is the ramdisk . ramdisk full esxi
Definition: A ramdisk is a volatile memory (RAM) storage area formatted with a file system (typically tmpfs or visorfs ). It is created during boot and resides entirely in physical memory. Purpose: ESXi uses multiple ramdisks for transient, high-speed data that does not need to survive a reboot. This includes:
System logs ( /var/log ) Runtime state files ( /var/run ) Core dumps (if configured for local crash dump) Scratch partition operations (if no persistent scratch location exists) Temporary VMX process data
2. Why "Ramdisk Full" Occurs When an ESXi host reports ramdisk full (commonly seen in logs or via vdf -h ), it means one of the memory-backed file systems has reached its capacity limit. Common root causes: | Cause | Description | |-------|-------------| | Excessive logging | Verbose debugging enabled, repeated error loops, or misconfigured syslog generating GBs of logs. | | Missing persistent scratch | If ESXi cannot find a persistent datastore for scratch (e.g., local VMFS volume), it uses the ramdisk, quickly filling /var/run or /tmp . | | Memory pressure | ESXi dynamically sizes ramdisks based on available RAM. If the host is memory-constrained, small ramdisks fill faster. | | VMX process leaks | A misbehaving virtual machine’s VMX process may write large temporary files into the host’s ramdisk. | | Active core dumps | If a PSOD (Purple Screen of Death) occurs and core dump is directed to a local ramdisk, it can consume multiple GB. | | Shell command outputs | Redirecting large output from esxcli or vsish commands directly to a file inside /tmp or /var . | 3. Symptoms of a Full Ramdisk When a ramdisk fills, ESXi behavior degrades in subtle but dangerous ways: When an ESXi ramdisk becomes full, it often
Hostd (vCenter agent) fails – Unable to write state files; host becomes unmanageable from vCenter. SSH login fails – fork: Cannot allocate memory or No space left on device . Logs stop updating – Troubleshooting becomes blind. VM operations fail – Powering on, migrating, or taking snapshots may fail due to inability to write lock files. HA/DRS issues – Heartbeats may fail; host may be falsely declared isolated or failed.
Example log entry (vobd.log): Hostd.ERROR: Failed to write to /var/run/vmware/hostd/hostd.log: No space left on device
4. Detection and Diagnosis 4.1 Check Ramdisk Usage Access ESXi shell (SSH or DCUI) and run: vdf -h Symptoms of a Full ESXi Ramdisk vCenter Alerts:
Look for filesystems with tmpfs or visorfs and Use% approaching 100%. Typical mount points: /tmp , /var/log , /var/run , /scratch 4.2 Identify Largest Files du -sh /var/log/* | sort -hr | head -20 du -sh /tmp/* | sort -hr | head -20 find /var/run -type f -size +50M -exec ls -lh {} \;
4.3 Check Scratch Configuration esxcli system settings advanced get -o /Scratch/ConfigCurrentScratchLocation
