Drives are the component that wears out first in a homelab, and the one that puts data at risk when it fails. An SSD that is perfect for a laptop can wear out quickly under a hypervisor's load, and a cheap hard drive can turn an array rebuild into an endless operation. It is worth choosing according to use, not just price per gigabyte.
SSDs: the specifications that really matter
Endurance
Flash memory cells withstand a limited number of write cycles. Manufacturers express lifespan in two ways:
- TBW (terabytes written): how many terabytes can be written during the warranty;
- DWPD (drive writes per day): how many times a day the full capacity can be rewritten throughout the warranty period.
A 1 TB consumer SSD typically states a few hundred TBW; write-oriented enterprise models reach far higher values. A hypervisor with ZFS, logs, databases and virtual machines writing constantly can use up endurance faster than you expect. The good news is that you can measure it: SMART data reports data written and the percentage of life used. Checking it after a month of operation gives a realistic estimate of lifespan.
Power-loss protection
Many enterprise SSDs have PLP (power loss protection): capacitors that, in a power cut, supply enough energy to write the data still in the drive's cache to flash. This lets the drive acknowledge synchronous writes safely and much faster. For a ZFS SLOG device or databases with many synchronous writes, the performance difference is considerable.
DRAM and cache
DRAM-less SSDs, or those with a small SLC cache, are fine for light loads but can collapse in performance during long, sustained writes, such as a virtual machine migration or a backup restore.
Used enterprise SSDs: an opportunity worth weighing
On the second-hand market you can find enterprise SSDs retired from data centres, in SATA, U.2 or 22110 M.2 formats. They often have huge endurance and PLP at attractive prices. Before buying:
- ask for or check the SMART data: power-on hours, data written, remaining life percentage;
- check the form factor: U.2 drives need an adapter or a compatible backplane;
- consider power draw and heat, often higher than consumer models;
- update the firmware if the manufacturer provides it.
Hard drives: CMR and SMR
For storing large amounts of data, hard drives remain cheaper. The fundamental distinction is the recording technology:
- CMR (conventional magnetic recording): tracks are separate, each sector is rewritten independently;
- SMR (shingled magnetic recording): tracks overlap like roof tiles to increase density; rewriting one area means rewriting neighbouring tracks too.
SMR drives work well for sequential writes and archives that rarely change, but under prolonged random writes performance can collapse. During a RAID rebuild or a ZFS resilver, this behaviour can stretch times enormously or trigger timeouts. For NAS units and redundant arrays it is prudent to choose CMR, checking the datasheet of the exact model: the same commercial family can include both technologies.
Other criteria for hard drives
| Criterion | What to check |
|---|---|
| Class | NAS or enterprise models, designed to run 24 hours a day |
| Rotational speed | 7200 rpm is faster but noisier and hotter than 5400 |
| Noise | high-capacity enterprise models can have noisy head movement |
| Annual workload | stated in TB per year in datasheets |
| Warranty | often longer on NAS and enterprise lines |
Buying sensibly
A few habits reduce the risk of simultaneous failures:
- do not buy every drive in an array from the same batch: drives made together can fail close together; buying from different shops or at different times helps;
- test new drives before trusting them with data: an extended SMART test and a full surface write bring early defects to light;
- keep a tested spare, so replacement can start immediately;
- label each drive with its serial number and position, so you replace the right one.
An example layout
In my work a typical layout for a home homelab is this: two PLP SSDs in a mirror for the system and virtual machines, two or more CMR hard drives in a mirror or RAIDZ2 for the archive, and a backup copy on separate drives. Each tier has the right drive for its load.
In short
- For SSDs, endurance, PLP and behaviour under sustained writes matter, not just peak speed.
- SMART data after a month of use shows how long an SSD will really last.
- Used enterprise SSDs offer endurance and PLP at a good price, once checked.
- Choose CMR hard drives for NAS units and redundant arrays, checking the exact model.
- Different batches, initial tests and a ready spare reduce risk.
