Computer Running Slow? Finding What's Using Your Disk Space

LIMEHAWK - Managed IT

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Space identified

98 GB recoverable

Incident

Ticket came in as "my computer is really slow." Remote user, 256 GB laptop. Classic symptoms: programs taking forever to launch, browser freezing, Outlook beach-balling. They'd already rebooted three times and called back.

We pulled diagnostics through RMM. Task Manager — nothing abnormal. CPU and memory normal. Performance counters fine. Then we checked the capacity metric: C: drive had 2.1 GB free of 256 GB. The user had no idea the disk was full. Now we needed to find what was eating 250 GB without scheduling a remote session and asking them to sit there watching WinDirStat scan for 20 minutes.

WHY FULL DISKS CAUSE "SLOWNESS"
Users almost never connect "disk full" with "computer slow." They see slowness and think virus, bad hardware, or "needs more RAM." The actual problem is their 47 GB of vacation videos sitting in Downloads.

- no room for swap: Windows can't expand the page file when RAM is full
- no room for temp files: applications crash when they can't write temp data
- no room for browser cache: Chrome and Edge constantly write and delete cache files
- Windows Update stuck: can't download updates, constantly retrying in the background

Why traditional analysis doesn't scale

Once we'd identified the disk was full, we had to find what was eating the space. The usual options all had problems:

- remote desktop + WinDirStat: requires user coordination, 15 to 20 minute scan, GUI that locks up mid-scan
- PowerShell Get-ChildItem: single-threaded, takes 30+ minutes on a full drive, no progress indication
- Windows Storage Settings: only shows categories like "Apps" and "Documents" — not actionable
- ask the user: "I don't know what's taking space, that's why I called you"

We needed something that could scan fast, run silently via RMM, and dump actionable output to the RMM logs without any user interaction.

Resolution

Built a script that downloads gdu (a fast Go-based disk analyzer) on-demand, runs a parallel scan, and outputs the largest directories to the RMM log. No pre-installation, no user interaction, results in 30 to 60 seconds.

Why this works

gdu is purpose-built for this use case. Single static Go binary, no dependencies, nothing to install on the endpoint long-term.

- parallel scanning: uses all CPU cores — scans 256 GB in 30 to 60 seconds vs 20+ minutes for WinDirStat
- hash verification: SHA256 checked before execution, prevents supply-chain issues from a compromised download
- non-interactive mode: the -n flag outputs clean text that drops straight into RMM logs
- self-cleaning: downloads on-demand, cleans up after — no permanent footprint on the client machine

What we found: the user's Downloads folder was 67 GB. Five years of accumulated installers, zip files, and Teams/Zoom meeting recordings they'd forgotten about. AppData\Local\Microsoft\Teams had another 23 GB of cached meeting videos. Browser caches totaled around 8 GB. All of it invisible to the user, all of it safe to clean up.

Outcome

Scan completed in 43 seconds. We identified 98 GB of recoverable space across Downloads (67 GB), Teams cache (23 GB), and browser caches (8 GB). Sent the user a summary email with the specific folders to clean out. They deleted 85 GB themselves (mostly Downloads), and we ran our automated disk cleanup script for the rest. Machine went from "painfully slow" to normal in about 15 minutes, with zero remote sessions and zero user time spent watching a scan bar.

- scan time: 43 seconds (vs 20+ min for traditional tools)
- space identified: 98 GB of recoverable bloat
- user interruption: 0 minutes, fully background

Key takeaways

Takeaway

"slow computer" tickets are often disk space issues in disguise — check capacity first before deeper diagnostics.

Takeaway

gdu's parallel scanning is 10x to 20x faster than traditional tools — critical for remote support.

Takeaway

Downloads and application caches are the #1 and #2 space hogs on user machines by a wide margin.

Takeaway

self-deploying tools beat pre-installed ones for RMM — no maintenance, always available, never stale.

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