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Samsung's SSD 840 Read Performance Degradation Explained
An anonymous reader writes with a link to TechSpot's explanation of the reason behind the performance degradation noticed by many purchasers of certain models of Samsung SSD (the 840 and 840 EVO), and an evaluation of the firmware updates that the firm has released to address is. From the piece, a mixed but positive opinion of the second and latest of these firmware releases: "It’s not an elegant fix, and it’s also a fix that will degrade the lifetime of the NAND since the total numbers of writes it’s meant to withstand is limited. But as we have witnessed in Tech Report’s extensive durability test there is a ton of headroom in how NAND is rated, so in my opinion this is not a problem. Heck, the Samsung 840 even outlasted two MLC drives.
As of writing, the new firmware has only been released for the 2.5” model of the SSD 840 EVO, so users of the 840 EVO mSATA model still have to be patient. It should also be noted that the new firmware does not seem to work well with the TRIM implementation in Linux, as this user shared how file system corruption occurs if discard is enabled."
Apparently the new firmware now advertises that it supports queued TRIM, when in fact it doesn't https://bugs.launchpad.net/ubu...
The old firmware did not advertise queued TRIM support, so it wasn't an issue. The solution is a kernel patch to blacklist queued TRIM on all Samsung 8xx drives.
Say you bought the 1Tb version (which is big for an SSD).
In this case, you rewrite it six times a year. That's 6Tb of write. That's...well... pathetic compared to the write expectancy of an SSD anyway.
So, actually, it's not that big a deal at all.
Most drives sold in the world today don't have power loss protection either.
If it matters to you, you put that stuff in the controller, not the drive.
Goodness me.
We had this problem back in the 1970s/1980s with floppy disks!
When the disc drive writes to a part of the surface of the disc it energies the magnetic particle to saturation. This ability of the material to keep so much of its original pulse of energy was called the clipping level of the floppy.
As soon as the area is energised, it starts to decay (hopefully) very slowly over time. Once it decays below 40% of the energy originally given, that bit is lost and data is lost.
Some cheap floppies had a nasty low clipping level as they'd use cheap materials, over time of say a year the area that hasn't been rewritten to would decay and that bit was then unreadable. You lost that data. We had various programs that would take the 8", 51/4" and 3.5" floppies and read then rewrite the entire disk to ensure that the disc was refreshed. As I worked in Ferranti for the UK space and military, I could ask the likes of TDK,Maxell, etc. what the clipping levels of their discs were. Something the public didn't have access too.
If the sellers wouldn't say, we simply didn't buy from them. Let me tell you most low-medium priced suppliers hide this value and we didn't do business. Glad to say the top disc suppliers were always open and we'd buy discs with an over 80% clipping level!
With these MLC SSDs the voltage level is very important. It'll decay over time, nothing can stop it.
Judging from the kernel's blacklist, queued TRIM does cause issues on quite a few SSDs, the 840EVO just did not announce that capability before the patch and now does (but cannot do it), and hence the problem. The kernel folks are now adding all Samsung 8xx to the blacklist, which will likely fix the issue. As Windows is traditionally behind in these areas it may just not use queued TRIM at all. I do hope that Samsung adds (more) Linux test systems to their qualification process now, though. Side-note: The 850PRO is apparently affected as well, but the kernel already blacklists it.
The conclusion here is that apparently getting SSD firmware right is a pretty big challenge and that SSD technology is still evolving. Also, not enough testing on Linux and likely not enough really smart people in the SSD firmware team. It is a learning process and the prevalent "clueless MBA bean-counter plague" will likely affect Samsung as well, just as it does any other large company.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.