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Everything I Know About SSDs

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Re: Everything I Know About SSDs

#71

Post by TremendousJudge »

winrid wrote: post #31
trymas wrote: post #21

Earlier quoted context omitted.

> Those things are modern car transmissions, .. Even though it may be off-topic, but could you elaborate on this a little bit more?

Not OP but in my experience people tend to have trouble comprehending systems of planetary gear sets. Although modern automatics are probably a bit easier to understand than old ones, especially CVTs? As long as you're ok with "the computer just triggers this solenoid.." rather than understanding a big hydrualic computer.

Modern automatic transmissions are actually manual transmissions with a robot moving through the gears as far as I know. However, they do a bunch of stuff that I don't understand like pre-engage the next gear so the switch is faster -- I have no idea how that works

Re: Everything I Know About SSDs

#72

Post by toast0 »

fareesh wrote: post #11

I wonder if anyone here has experienced something similar: I have a Samsung Evo 860 SSD. Sometimes after powering on my desktop the BIOS either "forgets" the drive (sets some other drive as primary boot drive) or doesn't recognize it at all. The non recognition issue goes away after I power off and power on. It's been this way for about 8 months. Happens every 1/15 times I power on. I've heard it may have something t…

I had an ssd/system combination that would not communicate at sata 3, and either the bios wouldn't try at sata 2 or it would timeout detection too soon after. If your bios lets you set a sata revision, it's worth a try (mine didn't, but I used a sketchy download of the AMI Bios Editor to adjust the default; I couldn't figure out how to use the editor enough to make the setting visible). And also maybe reseat the cables.

Re: Everything I Know About SSDs

#73

Post by bb88 »

mjw1007 wrote: post #59

I hoped it would discuss how SSDs cope with sudden power loss, but it doesn't seem to. I remember this page but I don't know of a modern update: http://lkcl.net/reports/ssd_analysis.html These days, if I want an SSD for my desktop and want to minimise the chance I have a disk problem and have to restore from backup, would I be better off with one "data centre" drive (eg Intel D3-S4510), or two mirrored "consumer" dri…

The big problem with one data center drive is that if that goes bad, you still lose all your data. You're assuming their marketing MTBF is correct.

They do make NVME raid solutions now -- with the advantage being that NVME can be faster than SATA. And there are various price points for the NVME drives depending upon speed.

This one from 2018 (not sure if it has full raid or uses VROC)(EDIT: it requires software raid)

https://www.pcworld.com/article/3297970/highpoint-7101a-pcie...

This one is cheaper but relies upon Intel VROC (which has been hard to get working on some mobo's apparently)

https://www.amazon.com/ASUS-M-2-X16-V2-Threadripper/dp/B07NQ...

In either case you're looking at max throughput of 11 gigabytes per second, which is roughly 20 times faster than SATA 3's 6 gigabits per second.

Re: Everything I Know About SSDs

#74

Post by kabdib »

rckoepke wrote: post #50
notacoward wrote: post #2

The part about filesystems is slightly incorrect. > The way the file system handles this is incompatible with the workings of NAND flash. That's true of most conventional filesystems, but log-structured filesystems are much more flash-friendly. That's why there has been a resurgence of interest in them, and also why a typical flash translation layer bears a striking resemblance to a log-structured FS. There are also…

> to an HDD all sectors are the same. Also I believe some humans, and (filesystems?) intentionally stored certain data towards the inside/outside of the HDD because the simple cylinder geometry allowed faster reads in those regions. However, I'm not seeing conclusive proof that modern HDDs show performance variation with respect to radius.

This is still very much true, to the point that game consoles will reserve areas of rotating media for different purposes, depending on speed (e.g., disk caches on the Xbox are on the outer tracks).

For optical media the layout of assets can be critical to the user experience. You probably want your startup assets located on the outer, faster tracks.

Re: Everything I Know About SSDs

#75

Post by ascar »

wtallis wrote: post #62
rckoepke wrote: post #50

Earlier quoted context omitted.

> to an HDD all sectors are the same. Also I believe some humans, and (filesystems?) intentionally stored certain data towards the inside/outside of the HDD because the simple cylinder geometry allowed faster reads in those regions. However, I'm not seeing conclusive proof that modern HDDs show performance variation with respect to radius.

> However, I'm not seeing conclusive proof that modern HDDs show performance variation with respect to radius. They definitely still do; it's fundamental to drives that run at fixed RPM but maintain high areal density across the entire platter. One of the 1TB drives I have lying around does about 183MB/s at the beginning of the disk, 148MB/s in the middle, and 97MB/s at the end.

I'm really interested in how you benchmarked that? Is there a "simple" way to specify the physical location on a HD data should be written to?

Re: Everything I Know About SSDs

#76

Post by hollander »

cbdumas wrote: post #30

I love a minimal, text-only website as much as the next crotchety HN reader, but a little bit of CSS goes a very long way in terms of readability. Edit: Upon further inspection I see that this page was designed to be hard to read. Very curious.

Use reader mode

Re: Everything I Know About SSDs

#77

Post by mxfh »

I get that it's meant to be subjective, but the premise makes it clear that it's an ongoing knowlegde collection, but for that some sources would be nice.

Currently my troubles with SSDs in PC/Server/NAS environment are a somewhat more practical, more about compatibility NVMe/SATA, M.2 key types, PCIe port bifurcation support vs PLX switches, none of them are even mentioned. Advice for this is notoriously hard to find, resorting to trusting rare and random forum posts is my state of knowledge progress there.

Re: Everything I Know About SSDs

#78

Post by wtallis »

ascar wrote: post #75
wtallis wrote: post #62

Earlier quoted context omitted.

> However, I'm not seeing conclusive proof that modern HDDs show performance variation with respect to radius. They definitely still do; it's fundamental to drives that run at fixed RPM but maintain high areal density across the entire platter. One of the 1TB drives I have lying around does about 183MB/s at the beginning of the disk, 148MB/s in the middle, and 97MB/s at the end.

I'm really interested in how you benchmarked that? Is there a "simple" way to specify the physical location on a HD data should be written to?

Hard drives generally use a fairly simple linear mapping between LBAs and physical location. Low LBAs are on the outer edge of the platter where transfer speeds are highest, and high LBAs are on the inner edge where speeds are lowest. Unlike SSDs, hard drives don't need wear leveling, so there's no reason to break from that pattern except in the relatively rare instance of damaged sectors.

At smaller scales, the layout of individual tracks can vary quite a bit, but that doesn't have as much impact on overall sequential transfer speed. See http://blog.stuffedcow.net/2019/09/hard-disk-geometry-microb...

Re: Everything I Know About SSDs

#79

Post by eMGm4D0zgUAVXc7 »

zozbot234 wrote: post #24
creeble wrote: post #13

Anyone know how TRIM works with Linux? I find myself copying entire partitions between SSDs from time to time, is there a utility to clear the destination SSD before copy? Is it possible to do the same for an SD card, so that writing a new Raspi OS to it doesn't do unnecessary garbage collection?

> I find myself copying entire/ partitions between SSDs from time to time, is there a utility to clear the destination SSD before copy? The way TRIM works, you don't need to trim blocks right before overwriting them. TRIM is for blocks that you aren't going to care about for quite some time, it essentially returns them to the SSD management layer for use as overprovisioning.

> The way TRIM works, you don't need to trim blocks right before overwriting them.

In my experience "blkdiscard /dev/DESTINATION_DISK" does improve the speed of dd'ing a disk to another one quite a bit though.

And that does make some sense IMHO: If the SSD's internal datastructure which keeps track of pages which hold user-data is empty then each write will consume less time for looking up if the specific sector is contained in the datastructure.

Re: Everything I Know About SSDs

#80

Post by mxfh »

bb88 wrote: post #73
mjw1007 wrote: post #59

I hoped it would discuss how SSDs cope with sudden power loss, but it doesn't seem to. I remember this page but I don't know of a modern update: http://lkcl.net/reports/ssd_analysis.html These days, if I want an SSD for my desktop and want to minimise the chance I have a disk problem and have to restore from backup, would I be better off with one "data centre" drive (eg Intel D3-S4510), or two mirrored "consumer" dri…

The big problem with one data center drive is that if that goes bad, you still lose all your data. You're assuming their marketing MTBF is correct. They do make NVME raid solutions now -- with the advantage being that NVME can be faster than SATA. And there are various price points for the NVME drives depending upon speed. This one from 2018 (not sure if it has full raid or uses VROC)(EDIT: it requires software raid)…

As stated, support for that one is not guaranteed, you need to first figure, out if your motherboard configuration supports lane bifucartion, otherwise it won't work, or only one of the installed keys.

Cards with PLX switches are are way to fix this if you cant upgrade your whole hardware, but the price point is a multiple of simple bifurcation cards, since you have to integrate a whole PCI switch on-card.

The architecture diagrams here are quite helpful:

https://www.qnap.com/en-us/product/qm2-m.2ssd

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