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Comment by vbezhenar | Hacker News Reader

Are there any consumer M.2 drives with guaranteed data protection (with capacitor or battery to flush all volatile data at power loss)? I did not find that kind of information in specs.

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I doubt any consumer M.2 drives will have power loss protection. The additional cost and PCB space required for the capacitors is a non-starter in consumer drives where every cent counts.

Server grace storage will specify if power loss protection is included on the board. You can usually identify the capacitors as well. For example, they are the yellow rectangles near the edge of this Intel SSD: https://ark.intel.com/content/www/us/en/ark/products/96932/i...

Note that the Intel drive with PLP is 110mm long, which is 30mm longer than most consumer M.2 SSDs due to the additional capacitors. This won’t fit on certain consumer motherboard.

> This won’t fit on certain consumer motherboard.

From diving into this recently in speccing out a budget system for myself, it looks to be mostly the lower end budget chipsets and motherboards that don't support it. At least that's what I've seen of the regular sized ATX boards, but it may be a different story for Micro-ATX or Mini-ITX.

The relevant info is always in the specs, and will look something like:

  M.2 Slots
    2242/2260/2280/22110 M-key
    2242/2260/2280 M-key

For each of those, the first two numbers are the width, the rest denote the length. So 2280 is 22mm x 80mm, and 22110 is 22mm x 110mm.

Consumer SSDs are very nearly defined as those that do not include the extra hardware necessary for such guarantees; the only other defining feature of a consumer SSD is the presence of low-power idle states. I'm not aware of any current or recent flash-based SSDs marketed at consumers that feature the same kind of power loss protection as enterprise SSDs.

Intel's Optane SSDs don't need power loss protection capacitors because they don't cache writes—their 3D XPoint memory is more or less fast enough to not require it. These drives correctly advertise that they do not have a volatile write cache. I have not encountered a consumer NVMe drive that lies about having a volatile write cache, but I have not attempted to test how they behave when the host requests that the write cache be disabled.

Consumer Crucial/Micron drives used to have enough capacitors on board to, at least in my understanding, never corrupt data on power loss (not sure if they flushed the cache, but I think they at least tried and guaranteed sectors wouldn't become unreadable/corrupted due to being partially written). They dropped this in later models, though, but I think they still claim they can guarantee non corruption/partial writes?

I stopped trusting Crucial when they released the P1 though. That QLC drive is terrible on every metric. Performance falls off a steep cliff once you do any writes at all, and often never quite recovers. Tail latencies are in the 1 second range, which is insane for an SSD.

These folks combine Intel 3D XPoint + QLC to deliver a two-tiered cheep storage solution: https://vastdata.com/

Intel's "Intel® Optane™ Memory H10 with Solid State Storage" is an Optane/QLC flash hybrid drive with an NVMe interface and capacities up to 1TB. It claims to offer enhanced power loss data protection:

https://www.intel.com/content/www/us/en/products/memory-stor...

I found this review which makes it sound pretty reasonable:

https://www.tomshardware.com/reviews/intel-h10-qlc-flash-opt...

The Optane half of the H10 doesn't need power loss protection capacitors, and the QLC half of the drive doesn't have room for them. Intel has stated that their caching software for that drive will sometimes send writes directly to the QLC half without buffering them on the Optane half, so the package as a whole does not offer enterprise-grade power loss protection and shouldn't be listed as such.

SLC cache looks like another consumer feature that not supported on enterprise drives maybe due to inconsistent performance.

Not "consumer", but the only M.2 SSD with 80 mm length (M.2 2280) I found that has power loss protection is this one:

https://www.kingston.com/en/ssd/dc1000b-data-center-boot-ssd

Rather interestingly, despite obviously having a bank of large capacitors and conspicuous advertising of power loss protection, the firmware on that drive identifies it to the host system as having a volatile write cache.

Last weekend my ThinkPad running ZFS on Linux on a Samsung non-power-loss-protected consumer SSD lost various files when it ran out of power (including the entire Thunderbird profile because its SQLite DB was corrupted).

I'm planning to replace it by the SSD linked above.

I was already aware of the power loss issue on consumer SSDs (from the 2013 piece http://lkcl.net/reports/ssd_analysis.html), but I wanted to see it happen for real. I guess I did now.

You'll probably experience a lot more unplanned power loss in your laptop by giving it a SSD that idles at 1.2W instead of one that idles in the mW range. And there's a real chance that it won't even solve your problem.

This does not answer your question, but wouldn't it be easier to get a cheap UPS with enough battery life to get your machine through additional 5 minutes of uptime?

Although I've had problems with hardware hanging so completely that it does not respond to the reset button, and the only option is to cut power, so UPS does not provide full protection.

UPSs are never really cheap, since when converting AC to DC to AC you lose a significant amount of power efficiency for your equipment. The funny part is the server PSU then converts back to DC power yet again. My understanding is that well optimized data centers distribute conditioned, battery backed DC power directly to devices to avoid those double conversion losses.

A small UPS will often have the equipment running directly on AC input power and only switch to the battery if the input power fails.

Oh, thanks for the correction. It seems I forgot that type existed or just never knew. Now I'm curious about the relative merits. I'd guess the transition is not as smooth and presents some kind of a risk that's unacceptable for critical infra.

The terms that describe those types are Line-interactive and On-line UPS.

E.g., https://blog.tripplite.com/line-interactive-vs-on-line-ups-s...

It'd be good if consumer UPSes had DC output for this reason. If only laptops could be standardized in terms of voltage requirements.

A lot of them are pretty similar; 19V - 21V seems quite common.

Until recently phones were standardized on 5V. Now, it's a mess again. :-(

I vaguely recall seeing someone modify their UPS for this in their "homelab", such that they were running a 12v cable modem, router and WAP off of the UPS battery pack directly somehow. They had dramatically longer run time from a full charge. (Well more than double, I think.)

Ooh, imagine a NUC or such small enough machine running off of USB-C Power Delivery. 65 Watt power budget easily. I guess a Raspberry Pi would count as that?

Then a battery pack could provide that, as DC.

The PSU will let you know in advance that power is going out. I think the interesting question is which SSDs have FTLs that can safely "park" in this time to a consistent state.

Is there a standard for PSU's about how long they provide power, that SSDs could design to?

> Is there a standard for PSU's about how long they provide power, that SSDs could design to?

Yes. The ATX power supply spec has timing requirements for the PWR_OK signal. As described on Wikipedia:

> The ATX specification requires that the power-good signal ("PWR_OK") [...] remain high for 16 ms after loss of AC power, and fall (to less than 0.4 V) at least 1 ms before the power rails fall out of specification (to 95% of their nominal value).

So power supplies are expected to continue operating through roughly a single missing cycle of AC power, but they only have to give the system 1ms of warning when power is going out. This signal would have to be delivered to the SSD by software in the form of a shutdown notification (a write to a particular NVMe register).

And now that I think about it, that shutdown notification mechanism probably warrants inclusion in the article.

I see, didn't even know that the original ATX spec made any promises, I guess 1 ms is "something", strictly speaking :)

I was hoping for a post-1995, more usable spec since we know that current PSUs often do provide power longer than 1 ms.

A single AC cycle would be 16-20 milliseconds which could already be doable if the SSD got the signal right away without OS involvement.

I'm not sure that bit actually comes from the original ATX spec; Wikipedia seems to indicate it showed up in ATX 2.31 in February 2008. It does also appear to be consistent with the very recent Intel ATX12VO spec.

Actually the Crucial MX500 SSD series had extra capacitors for power loss. Unfortunately they removed it for M.2.

That wasn't the same thing. Crucial SSDs always had volatile write caches. What their MX series and at least some of the NVMe drives offer is the guarantee that data already on the flash will not be corrupted by a write that's in progress when the power fails. But that doesn't affect the semantics of writes that may still be pending in the volatile write cache.

This potential failure mode is possible when storing more than one bit per flash memory cell, and using a multi-step process to program the cell voltage, and mapping the low-order bits of a cell's value to different LBAs than the high order bit. Drives need to have the capability to either complete or safely abort an in-progress cell program process so that the value in the high-order bit(s) isn't corrupted by an incomplete programming of the low-order bit(s). And this power failure problem isn't the only reason why SSDs need to be careful about leaving cells in a partially-programmed state.

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