Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

What we learned about SSDs in 2015

zdnet.com

Post reply on HN
Print view View original

61–70 of 111 posts

Re: What we learned about SSDs in 2015

#61

Post by derefr »

velox_io wrote: post #22

The most exciting recent development in SSDs (until 3DXpoint is released), is bypassing the SATA interface, connecting drives straight into the PCIe bus (no more expensive raid controllers). Just a shame hardly any server motherboards come with M.2 slots right now. The 4x speed increase and lower CPU overhead means it is now possible to move RAM only applications (for instance in-memory databases) to SSDs, keeping on…

If we can connect SSDs directly to the PCIe bus... why are there no cute little Thunderbolt flash drives that run at full NVMe speed?

Re: What we learned about SSDs in 2015

#62

Post by wtallis »

fleitz wrote: post #45
scurvy wrote: post #34

Earlier quoted context omitted.

My thoughts exactly. The article is quite inflammatory and tosses out some bold statements without really deep diving into them. My favorite: "Finally, the unpredictable latency of SSD-based arrays - often called all-flash arrays - is gaining mind share. The problem: if there are too many writes for an SSD to keep up with, reads have to wait for writes to complete - which can be many milliseconds. Reads taking as lon…

There is unpredictablilty in SSDs however, its most like whether an IOP will take 1 ns or 1 ms, instead of 10 ms, or 100 ms with an HD. The variability is an order of magnitude greater but the worst case is an is several orders of magnitude better. Quite simply no one cares that you might get 10,000 IOPS or 200,000 IOPS from an SSD when all you're going to get from a 15K drive is 500 IOPS

Best-case for a SSD is more like 10µs, and the worst-case is still tens of milliseconds. Average case and 90th percentile are the kind of measures responsible for the most important improvements.

And the difference between a fast SSD and a slow SSD is pretty big: for the same workload a fast PCIe SSD can show an average latency of 208µs with 846µs standard deviation, while a low-end SATA drive shows average latency of 1782µs and standard deviation of 4155µs (both are recent consumer drives).

Re: What we learned about SSDs in 2015

#63

Post by wtallis »

derefr wrote: post #61
velox_io wrote: post #22

The most exciting recent development in SSDs (until 3DXpoint is released), is bypassing the SATA interface, connecting drives straight into the PCIe bus (no more expensive raid controllers). Just a shame hardly any server motherboards come with M.2 slots right now. The 4x speed increase and lower CPU overhead means it is now possible to move RAM only applications (for instance in-memory databases) to SSDs, keeping on…

If we can connect SSDs directly to the PCIe bus... why are there no cute little Thunderbolt flash drives that run at full NVMe speed?

Windows has had astoundingly bad Thunderbolt hot-plug support given that ExpressCard and CardBus existed. NVMe support for non-Apple SSDs under OS X can be problematic. Thunderbolt PHYs are expensive. USB 3.0 is fast enough for now, and USB 3.1 exists.

Re: What we learned about SSDs in 2015

#64

Post by Dylan16807 »

TeMPOraL wrote: post #41
ComputerGuru wrote: post #8

Kind of stupid to end with "Since CPUs aren't getting faster, making storage faster is a big help." CPUs and storage exist for completely disjoint purposes, and the fastest CPU in the world can't make up for a slow disk (or vice versa). Anyway, CPUs are still "faster" than SSDs, whatever that means, if you wish to somehow compare apples to oranges. That's why even with NVMe if you are dealing with compressible data e…

Ever tried to play a modern computer game? You never have enough RAM for stuff; a lot of content gets dumped onto hard drive sooner or later (virtual memory), or is be streamed from the drive in the first place. Having faster access helps tremendously. From my observation, actually most personal and business use machines are IO-bound - it often takes just the web browser itself - with webdevs pumping out sites filled…

I don't think I've touched a game on PC where you can't fit all the levels into RAM, let alone just the current level. Sometimes you can't fit music and videos into ram, but you can stream that off the slowest clunker in the world. A game that preloads assets will do just fine on a bad drive with a moderate amount of RAM. Loading time might be higher, but the ingame experience shouldn't be affected.

As far as swapping, you do want a fast swap device, but it has nothing to do with "Since CPUs aren't getting faster". You're right that it's IO-bound. It's so IO-bound that you could underclock your CPU to 1/4 speed and not even notice.

So in short: Games in theory could use a faster drive to better saturate the CPU, but they're not bigger than RAM so they don't. Swapping is so utterly IO-bound that no matter what you do you cannot help it saturate the CPU.

The statement "Since CPUs aren't getting faster, making storage faster is a big help." is not true. A is not a contributing factor to B.

Re: What we learned about SSDs in 2015

#65

Post by lsc »

wtallis wrote: post #56
lsc wrote: post #43

Earlier quoted context omitted.

edit: okay, I re-read what you said and yes, these won't support M.2 drives, if I understand what's going on here, and it's possible I still don't. (I have yet to buy any non-sata SSD, though I will soon be making experimental purchases.) I was talking about these: http://www.supermicro.com/products/nfo/NVMe.cfm Note, though, it looks like if you are willing to pay for a U.2 connected drive, you can get 'em with the…

Take a look at how much stricter the temperature and airflow requirements are for Intel's 2.5" U.2 drives compared to their add-in card counterparts. (And note that the U.2 drives are twice as thick as most SATA drives.) M.2 has almost no place in the server market. U.2 does and will for the foreseeable future, but I'm not sure that it can serve the high-performance segment for long. It's not clear whether it will re…

>M.2 has almost no place in the server market. U.2 does and will for the foreseeable future, but I'm not sure that it can serve the high-performance segment for long. It's not clear whether it will reach the limits on capacity, heat, or link speed first, but all of those limits are clearly much closer than for add-in cards.

No argument on m.2 - it's a consumer grade technology. No doubt, someone in the "cloud" space will try it... I mean, if you rely on "ephemeral disk" - well, this is just "ephemeral disk" that goes funny sooner than spinning disk.

But the problem remains, If your servers aren't disposable, if your servers can't just go away at a moment's notice, the form factor of add-in cards is going to be a problem for you, unless the add-in cards are massively more reliable than I think they are. Taking down a whole server to replace a failed disk is a no-go on most non-cloud applications...

Re: What we learned about SSDs in 2015

#66

Post by ersii »

burntwater wrote: post #54
lsc wrote: post #35

Earlier quoted context omitted.

uh, this shouldn't be voted down. Now, I don't use RAID for performance, I use raid for reliability, like parent said, and I've never actually been in a position where it would make sense, but people do use raid0 to increase performance. It happens, even if it's not nearly as common as using raid to prevent data loss.

High-end video servers used in the entertainment industry typically use RAID 0. My last project, for example, used 10 250GB SSDs in RAID 0.

What kind of video servers are you talking about? For ingesting from a feed/camera in? Streaming out video? Curious.

Re: What we learned about SSDs in 2015

#67

Post by bigiain »

toomuchtodo wrote: post #48
lsc wrote: post #35

Earlier quoted context omitted.

uh, this shouldn't be voted down. Now, I don't use RAID for performance, I use raid for reliability, like parent said, and I've never actually been in a position where it would make sense, but people do use raid0 to increase performance. It happens, even if it's not nearly as common as using raid to prevent data loss.

Back in the day, folks would RAID0 AWS EBS volumes to get the level of performance they needed (this was long before SSD EBS volumes).

Now you're making me feel old - when "back in the day" and "AWS" get used in the same sentence... :-)

Re: What we learned about SSDs in 2015

#69

Post by mirimir »

lsc wrote: post #35
tehwalrus wrote: post #29

Earlier quoted context omitted.

> RAID isn't about connecting drives, it's about not losing data. RAID-0 is used as a way to get faster performance from spinning disk drives, as you can return parts of each read request from different (striped) drives. You also get better write performance, as your writes are split across the drives.

uh, this shouldn't be voted down. Now, I don't use RAID for performance, I use raid for reliability, like parent said, and I've never actually been in a position where it would make sense, but people do use raid0 to increase performance. It happens, even if it's not nearly as common as using raid to prevent data loss.

I like RAID10. It's almost as reliable as RAID1, and you get about half the capacity and performance boost of RAID0. With four drives, RAID10 gives you the same capacity as RAID6. It's only ~30% slower, and it rebuilds much faster after drive failure and replacement. With more drives, you get 100% of added drive capacity for RAID6 vs 50% for RAID10, but rebuild time gets crazy huge.

Re: What we learned about SSDs in 2015

#70

Post by ScottBurson »

bravura wrote: post #39

I need an external disk for my laptop that I leave plugged in all the time. What is the most reliable external hard drive type? I thought SSDs were more reliable than spinning disks, especially to leave plugged in constantly, but now I'm not as sure.

I still don't trust SSDs as much as I do spinning disks. While neither kind of drive should be trusted with the only copy of important data, I would say that drives used for backup, or for access to large amounts of data that can be recovered or recreated if lost and where the performance requirements do not demand an SSD, might as well be HDDs -- they're cheaper, and arguably still more reliable. If the workload is write-heavy, HDDs are definitely preferred as they will last much longer.

While all disks can fail, HDDs are less likely to fail completely; usually they just start to develop bad sectors, so you may still be able to recover much of their contents. When an SSD goes, it generally goes completely (at least, so I've read).

So it depends on your needs and how you plan to use the drive. For light use, it probably doesn't matter much either way. For important data, you need to keep it backed up in either case. SSDs use less power, particularly when idle, so if you're running on battery a lot, that would be a consideration as well.

Post reply on HN