I purchased two WD Red SN700 500GB NVMe SSDs for my Synology 920+ running DSM7, opting to use just one in READ mode for Calibre and Plex libraries, plus Docker images. The installation was effortless. The upgrade significantly improved artwork loading speed, enhancing the media room experience, though movie playback remained unchanged. Despite Synology's compatibility warnings about WD products, the SSD works perfectly. With 15TB of storage, a single 500GB NVMe SSD proves ample for my needs. The spare SSD might find use in another NAS or computer. While a 256GB SSD could have sufficed, the extra capacity allows for future growth. Overall, this upgrade noticeably improved system responsiveness, particularly in media-heavy applications.

While the Samsung 970 EVO Plus is an excellent SSD, for NAS cache use, you might want to consider SSDs with higher endurance ratings. The WD Red SA500 or the Seagate IronWolf 125 are specifically designed for NAS systems and offer great durability.

I've used Synology's own SSDs, and while they're reliable, I don't think they're worth the premium price. You can get similar or better performance from other brands at a lower cost.

For your usage, I'd recommend at least 500GB. This will give you enough space to cache your most frequently accessed data, especially considering you're running Plex and some VMs.

As for optimization, make sure you're running the latest DSM version, as Synology often includes improvements to cache performance in their updates.

WD Red SN700.

After using 8x 2TB Samsung Evo SSDs in a RAID 10 NAS setup for several years, I've discovered that small writes in a NAS environment can accelerate SSD wear unexpectedly. Four to five of my NAS Evos failed at only 25-30% of their rated Terabytes Written (TBW), affecting both Evo 860 and 870 models rated for 1200 TBW.

While these SSDs are cost-effective and functional, be prepared for replacements after a couple of years of use. I've started switching to Intel D3-S4510s as replacements, which offer about five times the wear rating at a reasonable price.

This experience highlights the importance of understanding that not all write operations impact SSDs equally, especially in NAS environments where small, frequent writes can significantly reduce SSD lifespan compared to their rated endurance.

I use Samsung 870 EVO SATA III SSDs, works well and no problem yet.

For NAS setups, avoid consumer-grade SSDs. Choose NAS-specific drives from brands like Seagate, WD, or Synology. These are engineered for continuous operation in network storage environments, offering better reliability and performance for NAS applications.

Just get any NAS-specific drives.

I recently upgraded my DS920+ with SSDs, and I went through similar considerations. You’re right to weigh the differences between consumer-grade and enterprise SSDs. For reliability and endurance, the Samsung 970 EVO Plus is robust, but if you're heavily using it for virtualization and media streaming, you might want to consider the Synology SSDs. They tend to perform well and come with optimizations for Synology systems.

Regarding size, I went with 500GB SSDs, and it has been an ideal choice for caching purposes, with plenty of headroom. A 250GB SSD could work but might fill up quickly, especially if you're doing light virtualization alongside Plex streaming.

For optimizing your SSD cache, ensure that you set up the read cache for frequently accessed files and keep an eye on your cache usage stats. DSM provides good insights on this. Hope that helps!

Remember that the "best" SSD depends on your specific use case. If you're using them for general storage, any reputable SATA SSD will do. For caching, focus on drives with high endurance ratings. Always check Synology's compatibility list before purchasing!