Network Attached Storage, mixed drive types

Factual Questions
1

I see some NAS are being sold with e.g. 4x 3.5" bays, 2x 2.5" bays, and 2x M.2 SSD. I understand the purpose of the 3.5", but most 2.5" drives sold don’t match the capacity of 3.5", and SSDs certainly don’t. WD Red 3.5" currently maxes at 10 TB, and 2.5" only 1 TB.

Is the 2.5" included instead of 3.5" due to physical limitations (e.g. the CPU or fans filling the other inch)? I guess this would waste a considerable amount of space with RAID 5/6, but with proprietary software is more efficient. Can you set up a RAID 5 with the 4 3.5" and a second RAID 1 with the 2.5" drives?

What’s the m.2 drives for? Caching? I suppose the 2.5" could also be SSD in this case.

2

2.5" bays in storage hardware are primarily intended for SSDs. In this application, they are intended for tiered storage or caching. In older equipment, they were intended for very high speed hard drives and to increase drive density for performance and availability.

3

Thanks. Do the 2.5" and m.2 caches play well together or is it either/or - will m.2 throttle down in speed?

How crucial are cache drives for small-office occasional storage and backup?

4

What Cleophus said, with a couple of extra points:

While 3.5” drives are the right choice for sheer capacity, you’re a little off regarding the capacities of 2.5” drives—they get considerably bigger than 1TB. Western Digital’s 2.5” drives max out at 2TB, I believe, and you can get a 5TB 2.5”’drive from Seagate, though it’s 15mm tall rather than the laprtop-standard 9.5mm. But the 15mm drives fit in 3.5” drive sleds just fine, albeit most sleds require a cheap adapter.

2.5” SSDs are commonly available in up to 4TB sizes. But it won’t make sense to buy 2.5” SSDs much longer, and they’re restricted by the SATA interface to a nominal 6Gb/s. But watch out—so are some M2 drives.

What you want for maximum speed are NVME M2 drives. They’ll transfer about 2000 MB/s—that’s 16Gb/s, or about four times the real-world maximum of A single SATA SSD, and more than ten times the maximum transfer rate of a single spinning SATA hard drive.

MSATA M2 drives are fairly common, but they’re as slow as regular SATA SSDs. Many M2 slots will accept both MSATA and NVME M2 drives, so watch out.

(All of this is for consumer-level hardware. You can buy bigger, faster 2.5” enterprise drives, but these use the SAS interface, not SATA. Enterprise-level SSDs also have higher capacities and a unique interface).

The first question you need to answer is: “What do I want my NAS box to do?”

It used to be that four spinning disks in RAID 5 have you redundancy (in case of drive failure) and sequential read speeds that, over gigabit Ethernet (at about 110 MB/s in the real world) were similar to the speeds you’d see on a local drive.

Now, that’s painfully slow. I use my own NAS as a file server for things I don’t need in a hurry. I also use it for incremental backups for several different machines. It used to be that you wanted drive redundancy because spinning drive failures are so common. RAID1 or RAID5 ensure that you can get to your data even if a drive in the array dies.

But SSDs are reliable enough that availability isn’t a big concern for me. My NAS is in flux right now, but eventually it will have the following storage devices:

  • One small NVME drive for the OS
  • One 2TB NVME SSD for serving files
  • One 4 TB 2.5” drive for incremental backups of local files, including those on the NVME SSD, as well as incremental backups of machines on my network, and
  • One 8 TB HDD for incremental backups of the 4 TB drive

There used to be a fair amount of geek prestige in having, say, 8-12 TB of RAID5 (or whatever) storage at home, but big, fast hard drives consume 6-10 watts each much of the time. Six drives sucking down eight watts each cost me about $72/year to keep in operation. In my current setup, I only spin up my HDDs when it’s time to do a backup, and they’re spun down shortly thereafter. That saves a lot of power compared to a spun-up HDD array, and one NVME drive is substantially faster than a six-drive RAID0 array. Of course, I’ll need 10Gb Ethernet to take advantage of those speeds, but that hardware is getting cheaper.

5

I didn’t mean to write a novel in my post above; I’ll try to be more succinct.

As long as your NAS is on gigabit Ethernet, you don’t need to worry too much about cache directly. In most scenarios, you’d need 10-gigabit Ethernet (or a large number of concurrent users) to see much advantage from caching.

Besides, caching is largely to make up for the deficiencies of spinning-rust drives. You’d do at least as well to use SSDs for your main storage medium and gain some reliability in the bargain.

6

WD Red seems to max out at 1 TB, they have up to 10 TB listed but crossed out. I assumed that it was due to the combo boxes being shared between 2.5 and 3.5, but maybe they don’t make them anymore (?) Seagate looks like they go to 5 TB, but they still have QC issues last I checked.

I guess we don’t need it, but the issue is that we need to spend grant money and only can do so in a limited number of categories. First world problems.

7

What is your ultimate goal? If you’re simply trying to maximize the amount of storage capacity available, then there are other, less expensive, NAS units that have more 3.5" bays than the one you linked.

8

Just curious. This one is an example, most I’ve been looking at only take 3.5

9

Another reason for multiple different form factors in NAS devices for home use is that many people fill them with older drives, often ones removed from computers that were replaced.

Older, slower drives, but good enough for backups (and effectively free – paid for long ago). These drives are of various sizes, so the unit has spaces for all of them. (You can get adapters to fit 2.5" drives in 3.5" spaces, but this avoids that.)

10

That link shows that the device comes with “Qtier technology and SSD cache enable”, so yes, the SSD and m.2 drives can be used for caching.