If you’re anything like me, you’re constantly running low on storage.
Thankfully, storage has come a long way in the past two decades, and you can find some seriously high-capacity hard drives and SSDs on the cheap. I picked up nearly 6TBs of storage — two 1 TB SSDs and a pair of 2TB 7,200 RPM HDDs — during last month's prime day sale for about $250.
Sounds like a great deal, right? Well, no not exactly. As usual, the adage "you get what you pay for" comes into play here. Not every SSD or hard drive is created equal, and there are a lot of pitfalls to watch out for, especially when hunting for a deal.
Don’t go DRAM-less
One of the ways SSD vendors cut costs on their budget drives is by ditching the DRAM cache.
DRAM is important for a few reasons. The first is it holds the look-up table for the rest of the drive. Specifically, it knows exactly where on the NAND flash that your data is hiding. As a result, DRAM can dramatically improve random read and write performance.
DRAM also has the added benefit of reducing the wear on the drives. DRAM acts as a write cache, which allows the SSD controller to spread data more evenly across the NAND memory cells. This is called wear leveling, and as its name suggests it's designed to prevent memory cells from wearing out earlier than others. You can think of it like rotating your tires.
Unfortunately, in some cases DRAM-less SSDs can actually perform worse than a spinning hard disk, making them a poor choice for a boot drive.
This mostly applies to older, slower SATA-based SSDs like Western Digital’s WD Green drives or Crucial’s BX500 series.
DRAM-less NVMe drives are a little bit more complicated since their performance depends on a number of factors, including their total capacity, how large the SLC cache (simulated) is, and the kind of NAND flash used.
The WD Blue SN550 NVMe drive I picked up during Prime Day is still a DRAM-less model, but thanks to some black magic running under the hood, the drive performs exceptionally well despite the handicap. Some of this is thanks to the drive’s use of higher performance TLC NAND flash.
With that said, DRAM-less SSDs are best avoided altogether unless you plan on using them for bulk storage, and only then if you can find one for a significant discount.
Consumer drives have gotten bigger, cheaper and slower
It turns out that spinning rust has gotten an upgrade, or downgrade, depending on how you look at it in the last couple of years. Most consumer drives, like the 2TB Seagate Barracudas I nabbed for $55 apiece, have moved to what’s called shingled magnetic recording (SMR).
The technology has enabled drive makers to pack more data closer together by storing blocks of data like the shingles on your roof — one overlapping the other. SMR has allowed drive manufacturers to dramatically lower the cost of storage at the expense of significantly slower write speeds. And it’s why you can buy 8TB hard drives for less than $200.
If you don’t mind making concessions on write speeds — my 7200-RPM Seagate drives topped out at an average of 80 MB/s in long 100GB-plus file transfers compared to 150-200 MB/s when using a conventional drive — these drives are worth considering, especially for archival.
I should note that these drives are still pretty quick where it concerns read speeds. Seagate advertises sustained reads of about 220 MB/s and in my testing, that’s not far off. However, that’s for a 7200 RPM drive, and many of the larger capacity options out there are much slower, operating at 5400 RPM or less.
The RAID problem
So if these drives are good for archival, you’d think they’d be great for data hoarders like me.
Unfortunately, the same technology that enables these drives to store tons of data on the cheap, also makes them impractical for use in RAID arrays and a host of other write-heavy applications.
For those that aren’t familiar, RAID stands for redundant array of independent disks, and it’s a way of writing data across multiple drives to improve redundancy in the case of drive failure. In some cases, it can actually boost performance as a side effect.
Others, including Patrick from Serve the Home, have covered this at length, but in a nutshell, SMR drives don’t play nice with most RAID controllers or ZFS file systems. If you don’t know what any of that means, it’s probably not something you need to worry about. But, if you’re interested in learning more, I highly encourage you to check out his coverage here.
The big problem is if a drive were to fail in a multi-hard drive RAID array, it could take more than a week to restore the parity data to the new drive. And if a second drive fails during the restore process, you could lose everything.
The exception to this rule should, in theory, be RAID 1, which simply mirrors data between two or more drives.
And this is the crux of my problem. I had originally planned to use the drives in RAID 1 for added redundancy.
Unfortunately, I discovered that doing so introduced tremendous read and write penalties. I saw sustained write speeds fall from around 80 MB/s when using one drive to as low as 9 MB/s when in RAID 1. Meanwhile, read speeds, which should have been unaffected by the mirror, fell to 140 MB/s.
I suspect the RAID controller on my motherboard wasn’t playing nice with the SMR controller on the drives. If you know for certain, please share your explanation in the comments section below.
You get what you pay for
Ultimately, DRAM-less SSDs and SMR hard drives aren’t inherently bad, you just have to know what you’re buying and understand their pros and cons.
Given the steep discount I was able to get, and the fact most of my data requires long-term storage more than anything, I felt I made out okay.
Perhaps the biggest disappointment was the Seagate Barracudas. Had I know that any kind of RAID, including RAID-1, was going to handicap the performance to that degree, I would have grabbed a single 4TB drive or spent a little more and purchased a pair of Toshiba NAS drives.
The bright spot for me was the WD Blue SN550 NVMe drive. It performed far better than I would have expected for a DRAM-less SSD, so well in fact that I don’t have any problem recommending it to anyone who doesn’t need the fastest drive out there.
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What do you think? Share your thoughts in the comments below:
- What SSDs or hard drives do you use?
- Have you had any trouble with SMR HDDs or DRAM-less SSDs
- Do you think the trade-offs of these technologies are worth the lower price?
- Would you like to see more posts like this one?