Is the cache value of a NAS solid-state drive? I spent 430 yuan to buy a block as a cache, and after three months, I removed it and used it as a download drive

my N100 mini PC running the Feiniu system, it had two drives running: one 4TB Western Digital Red Drive for movies and TV shows, and one 2TB for Kuyu for miscellaneous downloads. Last year, a friend came to my house and saw it, immediately asking, "Why don't you plug in a solid-state as a cache?" Everyone online says the speed doubles when inserted." I was tempted by what she said, so I spent 430 yuan on a promotion to buy a Zhitai SC001 256GB, which was stuck in the cache for three months. Last month, I disassembled it—not because it broke, but because I realized that this thing doesn't work at all in my usage. Taking it apart as a Docker download drive is actually much better. This article breaks down the 430 yuan tuition fee and explains it clearly.

to get straight to the point: the cache speeds up repeated reads, not your downloads

many people (including myself that day) think "adding caching = speeding up," which is the biggest misconception. The working principle of caching is simple: the solid-state stores one of the most frequently used data on the mechanical drive, and next time it reads the same data, directly from the solid-state. Pay attention to the three characters "same portion."

you download movies from outside to the NAS, the data is new, but the cache doesn't have it. Just write it to the mechanical drive—the mechanical drive is as fast as it is, the cache can't help. You back up 5,000 photos on your phone, each one the first time you write them in, and the cache can't help. When you watch movies at home on foreign websites, your pace changes every time, and the reading locations are all over the place. A 256GB cache can't fit several terabytes of a movie library, so most chances are it still won't help.

then what kind of situation could I possibly help?" You read the same file over and over. For example, the configuration of a Docker container and database are read by the system every day, or if you use Jianying to mount a NAS and edit the same clip of footage every day. First, use this standard to weigh your own usage, then read on.

my three-month tests: three uses, three results

Before

caching, I ran the benchmark, then tested intermittently for three months after installing it. The device was an N100 mini PC + 2.5G network port (remember the check on NAS transfer speed? First, eliminate the network port bottleneck before discussing caching, otherwise testing would be wasted). The data is as follows:

have you seen that watch clearly? The only thing that really speeds up is "copying the same file a second time"—I barely do that a few times a year. The most frequently used daily tasks—downloading, backing up, and watching videos—are basically the same before and after. As for fast-forward lag, that's a matter of transcoding and network ports, not caching. I mentioned in Jellyfin that the N100 hardware decoding can handle it, but the lag is in response, not read.

By the way, Feiniu's cache is divided into three levels: "read-only," "read-write," and "read/write acceleration + power-off protection," with read-only by default. I had my reading and write mode on for a week, but once the home switched off. After rebooting, the cache rebuilt, and the NAS turned on for an extra four minutes, but still couldn't access it. Machines without UPS (Uninterruptible Power Supply) have read/write caches that are just planting mines for themselves, which many tutorials won't tell you.

which four types of people are truly wasting money on caching purchases

based on my observations over the past three months and the failures of friends around me, here are a few ways to use cache money directly to save money.

• library type NAS. A movie series worth several TB, switching to the next after watching each one, with only those small images on the poster wall being read repeatedly. A cache of hundreds of gigabytes against dozens of terabytes of libraries has a hit rate so low it's almost negligible.
• purely as a downloader . Downloads are mainly written operations; the cache is read or not written (read-only mode does not accelerate writes at all). Buying cache for downloads is the opposite direction.
• mainly your phone backup album. Every day, I backed up photos taken that day, all of which were new data. If you really want to speed up backups, the bottlenecks are the phone's WiFi and NAS ports, not the ones.
• all-solid-state NAS. You're already using all solid-state systems, what's the point of caching...... Don't laugh, some group members really have asked.

three situations where caching is truly useful

isn't completely rejected; I've seen caches spent where it matters most—there are only three types.

the first method: video clips and attached to a NAS as a material drive I know someone who works in wedding planning. His material library is two TB, and the same batch of materials is edited several times. He attached a 1TB SSD as a cache, and the Premiere project opened much faster. The core is "reading the same batch of files repeatedly," which happens to be based on the working principle of caching.

the second method, Docker container keeps getting more . Random read/write of small files like container images and databases is the worst scenario for mechanical drives (4K random reads on mechanical drives are less than 1MB/s, and SSDs can be hundreds of times faster). Later, I moved the entire Docker directory to this 256GB block, and the container started up smoothly and the database responded smoothly. I'll explain this in detail below.

the third type, multiple people visit the at the same time. If three or four people at home watch different movies at the same time, or you share it with relatives and friends, the mechanical drive's magnetic heads will freeze into slides, and cache and SSD thermal data can clearly save the day. If used by one person, you basically won't hit this bottleneck.

Where did

SSD go? It's better to take it apart and use it as a system drive

figured it out, I did three things to get half of the 430 yuan back.

first item, disable cache mode. Feiniu Storage Management removed the cache pool, leaving the 256GB block empty. Be sure to check all important data before disassembly. Don't change the data disk when disassembling the cache pool, but don't skip the habit of backing up before you start—I mentioned in the about backup, what does the '1' in 3-2-1 mean?

the second item, the entire root directory of Docker was moved to the solid-state state. Feiniu's Docker is installed by default in the mechanical disk space. I created a new solid-state storage pool, pointed the Docker directory over, and used the image, container configuration, and database all on solid-state. The effect is much better than just caching: after rebooting, the time it takes to hold a dozen containers has dropped from 90 seconds to around 60 seconds, and Jellyfin's poster wall loads visibly faster. This is the most stable use of SSDs on NAS— storing "small files that are frequently read randomly," rather than "caching large files that are read only occasionally."

the third item, the temporary directory of the downloader also points to the solid-drive. After the download is complete, move it to the mechanical drive. When downloading, write the SSD first to reduce long searching on mechanical drives, so downloads at night no longer creak (those who know Western Digital know the sound of the red drive).

If I had to do it all over again, how would I spend that 430 yuan

end with a pragmatic conclusion. If you're planning to add your first SSD to your NAS, follow this order:

in short: the essence of cache is 'using the SSD to serve mechanical drives for repeated reads,' and for most people, the bottleneck for NAS is simply not repeated reads. 430 yuan for 256GB, caching is mystical, Docker drives are a necessity—this has been my most valuable experience over the past three months.