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Comment by colechristensen | Hacker News Reader

Did he do any control studies with spinning disks?

I have my doubts that many of them would survive thousands of power cycles per day.

I've seen a few different models of 2.5" Enterprise SAS drives go through a similar test (as a control,) and they were perfectly fine with no corruption after around 2 weeks of reboots at approximately 10 minute intervals.

It's the SSDs that I worry about - some store their own firmware on the same NAND as the User's data, and allow it to become corrupted during power-loss events. Several cheap models won't last more than a couple days before they simply drop off the SATA bus and never come back.

There's probably not much of anything that would survive that many power cycles in a day.

The test is pretty pointless.

It's not pointless, just misrepresented. SSDs enable new classes of applications for high-performance, non-power-protected computers. With an SSD and Intel ULV CPU, I can put together a cheap high-performance computer with no moving parts and no batteries. That has the potential to be very robust and have an expected lifetime of decades, but only if the SSD is rock solid.

Which SSD is going to last for decades in a strenuous environment?

Intel, apparently

This test really doesn't prove that at all. There are vastly different factors between power cycling in a single day and long term continuous use. You can't take results from one and get any meaningful information about the other.

You're right. But it does show one way in which it's resilient. Given this information and what else I know about Intel SSDs, I would expect them to be the most resilient overall.

What if I have thousands of disks deployed, and I suffer a single power loss? What are the chances that at least one disk will contain corrupt data after such an event?

Instead of buying thousands of disks to test this scenario, one reasonable shortcut might be to repeatedly test a single disk.

Even a spinning disk can handle a few thousand power cycles in its lifetime, surely?

On power up, there's a pretty big spike in power usage as the controller gets its shit together. Normally, this is not an issue, since the SSD housing simply absorbs the heat and then goes about its business. The same holds true for spindle drives.

What this guy did was test the drives in a manner they weren't designed for. Sure, I can drop Corvettes off a 20 story building, then bitch about the results, but that wouldn't change the fact that my test was flawed from the onset.

All he did was subject something to an environment is wasn't designed for.

Sure, I can drop a Corvette from a 20 story building, but there's nothing to be gained when the crumple zone is packed into the tail lights.

Hu? Where should that spike in power usage come from?

It comes from the decoupling/filter capacitors used in the DC power circuit. When the power is turned on after a sufficiently long time these capacitors are all uncharged and appear as "shorts" to the power source thus drawing large amounts of current. This initial surge current drops off as the capacitors get charged.

Filter capacitors producing excessive heat due to inrush current? That would be bad filter capacitors indeed ;-)

The claim was that an SSD somehow converted more electric energy into heat immediately after power-up which would damage the SSD, so real consumption, not just a current peak that goes into storage for later consumption. Normal-ESR electrolytics might have a heat problem when used at a few kHz in switching applications, but certainly not at 0.1 Hz.

It's long been standard practice with tantalum filter capacitors to feed them through an inductor or at least a resistor to prevent inrush current failures. That, and/or you derate the crap out of them when you design the board. Newer drives are probably using multilayer ceramics that can put up with just about any abuse including inrush.

Executive summary: powerup stress is not an issue unless the drive was designed by a moron.

From what they said about these reading sensor data, I'm picturing a factory, industrial, or field type scenario. I'm picturing a very small embedded computer with some sensors attached and an internal ssd. Referencing a 1.5gb OS like they did makes me think they just have a normal OS installed, but it's entirely possible that they have a modified kernel and fast boot process.

Essentially, it sounds like they have a single unit that gets turned on, gathers sensor readings, and then get turned off. I'm guessing these are not handheld devices, otherwise they most likely would have a battery attached. If a non 24/7 factory, these could be turned off with the rest of the assembly line by someone throwing breakers off on the way out (very common).

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