How to choose a NAS hard drive? I've bought Cool Wolf, Galaxy, and Red Plate for five yuan, but the first one fell into the trap of stacked tiles

the year I installed my first NAS, I bought a 4TB Western Digital Red Drive for a bargain, model WD40EFAX. Daily use is perfect, with read/write speeds around 170MB/s, quiet, and low heat generation. Until one day, I pulled out a drive to simulate a fault and did a RAID rebuild. The progress bar had been stuck at 78% for a whole day and night, and the speed dropped from triple digits to less than 10MB/s, that I started investigating what was really going on with this model.

first distinguish between CMR and SMR—I hit this pit on my first disc

mechanical hard drives are divided into two types based on recording methods. CMR (traditional magnetic recording) tracks lie side by side, undisturbed by each other, and you can write whatever you want to modify. SMR (Tile Stacking Logging) To fit more capacity onto the same platter, the tracks are stacked like roof tiles. When writing new data without conflicts, everything works fine. But if you want to rewrite the stacked tracks, the hard drive must first read out the surrounding data for temporary storage, then put it back after writing. Sequential read/write is not inaccurate at all; random small writes are a disaster.

The

pitfall was before 2020, when Western Digital quietly used SMRs on some red drives from 2T to 6T, with EFAX suffixes (like my WD40EFAX, WD30EFAX, WD60EFAX), and the specs didn't mention it at all. Later, when Synology users set up RAID, they found rebuild was so slow that it failed due to timeout, causing a major scandal. ServeTheHome conducted a comparison test with CMR drives, and found that SMR drives have a 13 to 16 times higher risk of error in RAID rebuild scenarios involving continuous mixed read-write reads and writes. Western Digital publicly apologized back then and released a CMR/SMR model comparison chart, and only then did the newly released Red Drive Plus (with EFZX suffix) fully switch back to CMR.

principle is actually simple: the SMR drive has a 20-30GB media cache that stores the data you write first. Before the cache is full, the speed looks good, but once it's full, you have to do the "read, modify, and write" actions on the spot, which directly drops the speed. RAID reconstruction happens to be several hours of nonstop mixed read/write, hitting the gun barrel the most.

So the first thing I do when buying now is check CMR. Here are three quick notes: Seagate CoolWolf covers all CMRs, with black and white text on the official website, so no worries; Western Digital recognizes the tail end, buy EFZX, dodge EFAX; Large-capacity drives above 8TB are basically helium-powered CMRs, making it hard to even step on the tiles. If you want to understand the RAID rebuild process, you can check out my previous article on how to choose RAID mode and how to calculate rebuild time.

What exactly is the difference between

Cool Wolf, Galaxy, and Red Plate? One table explains it clearly

I've bought these three major series for five yuan in total, so I've helped you sort out your positioning:

noticed? The pattern is simple: a regular NAS drive comes with a 3-year warranty, while Pro-grade and enterprise drives have a 5-year warranty , with a price difference of about 100 to 200 yuan. There's also a counterintuitive fact: companies buying Galaxy for the same capacity are often dozens to a hundred yuan cheaper than Cool Wolf Pro because companies purchase large quantities and channel prices are lower. In other words, the more you spend on the warranty, the more durable you can buy a more durable wheel—the trade-off is noise.

How noisy is

Milky Way? My 16T Galaxy chip has just over 20dBA when idle, and once you find it, it goes straight to 30dBA. If you put it in the bedroom, someone is stirring beans at the bedside. Later, I replaced my main photo drive with Cool Wolf (both Idle and Xundao were around 21dBA), and the Galaxy removed the weak current box as a download drive, so I got both. How to control noise? I wrote a special article NAS Noise Modifications, and the selector, shock pads, and fan settings all went down by 9 decibels.

capacity? The desserts are located at 8T and 16T

hard drives, the larger the capacity, the cheaper it is per TB, but it's not about maxing out the drive blindly. Based on the price I bought (rounded per TB): 4TB is about 600 yuan, 150 per TB; An 8TB is about 1100, or 137 per TB; A 16TB costs just over 2000, with each TB selling down to around 125. Capacity doubled, unit price dropped by one tier—4T is the least cost-effective tier in the entire tier.

don't just look at the unit price; two practical constraints are more effective. First is the bay slots: two machines with two bays of 4TB are installed in RAID1, but the usable capacity is only 4TB, costing two portions; It's better to just use an 8TB single drive and use the old hard drive for cold backup. How to plan storage spaces based on home data volume? I have carefully calculated in this article buying two or four trays. Second, the cost of expansion: replacing a large drive in a NAS isn't just about copying and pasting. System migration, shared directory orientation, and Docker mounting paths all have to be adjusted accordingly. My 4TB to 8TB upgrade took me half a day, and I'll record the process in disk swap and migration article. The first time you buy the capacity is enough; the second time you want to upgrade, the articles you read are different.

my suggestion is simple: start 8T, and 16T is the dessert . Units priced below 8T are not cost-effective and still occupy market space, while units above 16T (20T, 22T) start to rise again, and they encounter another problem with helium disks, which will be discussed below.

second-hand corporate properties are really attractive, but I only bought under these three conditions

a retiring enterprise property from mining farms and machine rooms, a 16T second-hand price is 1,230 yuan, less than 80 yuan per TB, half the price of brand new. At this price, buying a brand new one only gives you an 8T Cool Wolf, which is quite tempting. I have a second-hand Galaxy 16TB myself, and I've used it as a download drive for over a year without any issues. But I set three rules for myself and didn't touch any of them:

premise first: only install data that can be lost. downloaded movies, TV series, and system mirrors—if you lose them and can reload them, keep them on a second-hand drive; Family photos, work documents—these are things that would hurt if lost, so not a single one is given. Data security depends on backup strategies, not on hard drive age. This bottom line cannot be left to chance.

prerequisite two: get a medical check upon arrival. second-hand company drive for over 40,000 hours of electric driving, which means running nonstop for four or five years. The first thing I did after buying it was check the SMART power-on time and remapping sectors, then run it once to check the full drive write zero. My 16T lasted over 17 hours and only dared to install it after passing once. The specific commands and criteria for testing are in this New Hard Drive Full Disk Inspection —just copy them as is.

prerequisite three, the channel must be able to return or exchange. only buy those that support seven-day no-questions, refurbished labeled plates, and slag from unknown sources (the kind that costs 700 yuan for 14T), don't even give them away for free. After receiving the stock, first check the brand's official website for the serial number to see if the warranty status matches the sales area. If not, you can return it directly.

By the way, you should also monitor the health of second-hand drives while they're in use. If the number of sectors to be mapped and the number of sectors to be mapped only rises and never falls, that's a sign of bad luck. In my article on hard drive bad market warning signs I listed five signals and red and yellow card judgment tables. For old markets, it's recommended to check them once every quarter.

helium disc and a few easily overlooked little things

8T large-capacity disks above the disk, the disk cavity is filled with helium instead of air, resulting in low resistance, low power consumption, and more platters that can be stacked. But helium discs have a fatal flaw: once leaks, they have no repair value . You can open the air disc lid and swap the head for rescue, but if the helium disk opens the cavity, the helium will run away. The data recovery quote is ridiculously expensive and may not work. Therefore, second-hand helium disks must strictly follow the previous three rules. SMART has a Helium Level indicator (supported by some models); if the value is below 100, you have to start backing up your data.

there are a few small incidents where someone has paid tuition with real money:

First, don't buy a 2.5-inch NAS drive. For 4T and above, 2.5-inch mechanical drives either don't exist or are ridiculously expensive, and the RPM is only 5400. Installing a NAS is obediently 3.5-inch.

second, buy two RAID blocks of the same capacity, and try to split the orders into different batches. Disks from the same batch have the same innate defects, and the chance of them failing together is even higher. This is a matter of probability, not mysticism.

third, the phrase "enterprise-level" is worthless on e-commerce pages. Both labeled and refurbished discs love to use this term, but they recognize the model but not the slogan: Galaxy recognizes Exos, Western Digital enterprise discs recognize the HC series, red discs recognize EFZX suffixes.

Fourth, after setting up a RAID, you can rest easy. RAID prevents broken drives, not accidental deletion and ransomware. Choosing Btrfs with snapshots for the file system can save most slips. I've broken down this in my ext4 or Btrfs article.

just copy the script and copy it

have said so much, here is the conclusion for you:

order of purchases is also laid out: first decide capacity based on data volume (think twice as much; if 2TB is 2TB, buy 8TB), then check model and confirm CMR, then choose a channel (brand new depends on price and warranty, second-hand depends on returns and exchanges), get a physical check before installing it, and think through backup strategies before installing it on the NAS. In the end, it comes down to one thing: hard drives are consumables; they need to be replaced every five or eight years. You can buy cheap drives, but your data must be backed up by backups.