I spent longer than I’d like to admit troubleshooting latency issues on my workstation before realizing the obvious: I was running Claude Code and Gemini CLI off an 8TB mechanical hard drive.

Yeah.

The Symptoms

Every time I’d start a coding agent session, the whole system would hitch. Not just the agent - Windows itself would stutter. Explorer would hang. Typing in other applications felt sluggish. I went through the usual suspects: memory pressure, background processes, Windows being Windows.

It was the spinning rust.

Why HDDs Kill Agent Performance

Modern coding agents don’t just read your code once. They’re constantly crawling, indexing, writing to local SQLite databases, updating caches, running git status and ripgrep in the background. Thousands of small I/O operations per minute.

A mechanical hard drive handles maybe 100 IOPS. An NVMe SSD does hundreds of thousands. Orders of magnitude.

When an agent builds its context index, an HDD’s read head is physically moving back and forth across the platter trying to keep up. Disk thrashing. That grinding sound. System-wide lag.

The Fix

My workstation is a… well, basically it’s a Lenovo ThinkStation P520 (you know what this actually is, friends). Solid machine, but all my M.2 slots were occupied. So I picked up:

  • Ainex AIF-09 (about ¥1,380) - A PCIe-to-M.2 adapter card. Supports both NVMe and SATA M.2 drives, though I’m just using the NVMe slot. I should’ve grabbed the AIF-11 instead - it has an integrated heatsink, and NVMe drives run hot under sustained random writes. Coding agents are sustained random writes.
  • WD_BLACK SN850X - Overkill for PCIe 3.0 slots, but the IOPS and endurance rating justified it.

Under ¥20,000 total.

The Result

The stuttering is gone. Agent indexing happens in the background without me noticing. Time-to-first-response dropped considerably.

I should’ve known better. Modern dev tools assume near-instantaneous disk access. But I had this big 8TB drive sitting there, plenty of space, and I just… didn’t think about it.

If you’re running AI coding agents on a mechanical drive and wondering why everything feels slow - there’s your answer. Even a cheap SATA SSD over USB 3.0 would help. An NVMe drive is better.

Sometimes the obvious answer is the right one.

-J