Scratch‑Disk SSD Allocation versus Smart Object Proxy for Lowering Photoshop RAM Usage

Direct answer

For 16-bit, multi-layer PSDs, allocating a fast SSD as Photoshop's scratch disk gives a more predictable reduction in peak RAM usage than converting layers to Smart Object proxies. The SSD method works regardless of how many large layers exist, while proxies only save RAM when many layers are replaced by low-resolution stand-ins.

Confirmed facts

• Photoshop uses the scratch disk as virtual memory when RAM is exhausted; a faster scratch disk lowers the latency of those swaps and reduces the effective RAM pressure.
• Enabling a Smart Object proxy replaces the full-resolution layer data in memory with a lower-resolution preview; it does not change the amount of data written to the scratch disk.

Likely explanation

Because the scratch-disk mechanism directly limits how much RAM Photoshop can consume before swapping, an SSD (or any fast drive) provides a steady ceiling on RAM usage. Smart Object proxies depend on the user-chosen proxy resolution and the number of layers converted; their benefit varies with layer count and bit depth, making the RAM savings less predictable.

Steps for this case

1. Open Photoshop -> Edit -> Preferences -> Performance.
2. Set the primary scratch disk to the chosen SSD (ensure it has >= 20% free space).
3. Work on a representative large PSD and watch the Memory Usage indicator in the Efficiency gauge; note the RAM value when the gauge drops below 100%.
4. To test the proxy method, revert the scratch disk to its original setting, then select the large raster layers, choose Layer -> Smart Objects -> Convert to Smart Object, and in the Properties panel set a low-resolution proxy (e.g., 1024 px).
5. Repeat the same workflow and compare the RAM usage reported by the Efficiency gauge.

If the SSD scratch disk shows lower RAM usage and higher efficiency than the proxy method, the SSD approach is preferred for that workload.

Storage speed influence

With an SSD, scratch-disk swaps are fast, so the RAM-saving benefit is realized without a noticeable slowdown. On an HDD, the same swap latency can become a bottleneck, making the proxy method comparatively more attractive if the SSD is unavailable or heavily fragmented.

Combining both techniques

When the SSD scratch disk already keeps RAM usage low, adding Smart Object proxies yields little additional RAM savings because the scratch-disk swap volume is already minimal. Conversely, if proxies drastically cut the in-memory layer data, the scratch disk may see fewer writes, but the RAM usage is already near the proxy-limited floor; thus the combined gain is typically no greater than the better single method.

Missing diagnostic detail: Please confirm that the SSD designated as the scratch disk has at least 20% free space; if free space is lower, the recommendation may change due to potential performance degradation.