There are a few secrets for longevity on an SSD.
One way, as Stephen notes, is reducing your writes (trim also helps with this, by the way).
Another way is to not use the whole drive. That is, don’t fill it up. That effectively gives you more ‘spares’ so that the drive may be able to reduce the ‘write amplification’ a little, and also perhaps have somewhere to write stuff even if the number of ‘bad blocks’ (for a fuller drive) would make the drive unusable.
Huh? What is ‘write amplification’? Well, it’s a ‘feature’ of SSDs caused (primarily) by the fact that the SSD is not arranged as LBAs (sectors). The smallest amount of the flash that can be erased is an erase block, which can be 1Mbit or more! And the smallest amount you can write is a ‘page’. (Pages tend to be 4k Bytes or more)
And you cannot write to an un-erased area – that is, once written a ‘page’ in the erase block, you cannot write it again without erasing first.
So, imagine you are filling up an erase block with sectors (512 bytes). Now lets say you have sectors 1-20 and 2000-2010 in it, and now its full. Now, you change what’s in sector 2000 and write it back.
The drive CANNOT write it back in that erase block (unless there is space at the end of the erase block, but then I just said it was full ;-)).
So, it has to ‘do something’ with that new sector. Sometimes it has to COPY the ENTIRE erase block into a NEW erase block, inserting the new sector’s worth of data.
So a single 512-byte write resulted in 100Kbytes (or whatever) being written to the flash!
So, a single write was amplified into what looked more like 200 writes! Ouch! Welcome to write amplification!
(And it gets even worse if there aren’t enough ‘spare’ (already erased but not written) blocks – you may have to copy other full or partially-full blocks around also!)
For some drives, they can do a better job if they have more spare blocks around – so, if your drive isn’t full you’ve got more spares (if the drive firmware views them that way). In addition, you may be able to run longer by having more bad blocks but not enough to have no non-bad blocks for the amount of data you have on the drive.
Now, a little bit more info about SSDs, followed by 2 disclaimers.
SSDs are made up of Flash. Flash comes in at least 3 varieties:
SLC – aka ‘Single Level Cell’, which means that you only store 1 bit per transistor cell
MLC – aka ‘Multi Level Cell’, which means you store 2 bits per transistor cell.
TLC – aka ‘Triple Level Cell’, which means (you probably guessed it) that you store 3 bits per transistor cell.
(As a very scary fact, my understanding is that a transistor cell holds, at maximum, about 100 electrons. So, for SLC there are 2 values represented by 0 to 100 electrons. (you can pretend that under 50 electrons means a zero and above that means a 1 and not be too far off the mark). For MLC, 4 values are represented by those same 100 electrons. For TLC, that’s 8 values, or a difference of only 100/8 electrons per different ‘value’!)
Now, the other critical thing is that Flash manufacturers ‘guarantee’ a maximum error rate across the entire chip until that chip reaches a certain number of ‘program/erase’ cycles (as described above). It is true that some chips will do MUCH better (We’ve seen, in our testing, an SLC chip run 1million P/E cycles before becoming unusable – when the factory only gives 100,000). But in any case, here’s my understanding of the PE numbers for the different technologies:
SLC: 100,000
MLC: 10,000
TLC: 1,000 (I think – its been a while since anybody mentioned this number to me)
Which speaks directly to Stephen’s comment about number of PE cycles (ok, he didn’t say PE, but that’s what he is actually referring to J).
However, you probably don’t want to seriously consider rushing out and buying SLC drives – they cost MUCH more than MLC drives (like, 10 to 100 times more). Just back up early, back up often (as you should do for ANY primary storage device!!!)
Disclaimer 1 – I work for a company that makes SSDs. The above is NOT professional advice. See a real SSD shrink for professional advice.
Disclaimer 2 – Due to our IT department’s method of handling email, at this time I can RECEIVE PLUG emails, but I cannot REPLY to them (and have them seen). So I’m BCC’ing people and hoping they reply all, so that you can see this. Otherwise, only 2 folks will read it.
Rusty
From: plug-discuss-bounces@lists.phxlinux.org [mailto:plug-discuss-bounces@lists.phxlinux.org] On Behalf Of Stephen Partington
Sent: Monday, February 29, 2016 9:45 AM
To: Main PLUG discussion list
Subject: Re: Upgrade old laptop with SSD
The lifespan will depend entirely on the number of Writes the drive will incur. The first thing you want to do once the Os is installed is to reduce this. If you have enough ram and are comfortable with nos wap go for it. If you want the backup i would suggest pushing swappiness all the way over so that it is used only if there is no ram.
Most SSD's will give you a 3 year warranty. Samsung with their Evo 850 drives and the new vnand are offering 5 year warranty. (they are also wicked fast).
That being said. with minimal writes I have seen older SSD's last for much longer than their supplied 3 year warranty (I have one that is pushing 6 right now).
With an SSD the general user experience will be pretty good, but Anytime you run updates it will still crawl, regardless fo the SSD :-)
On Mon, Feb 29, 2016 at 8:49 AM, Keith Smith <techlists@phpcoderusa.com> wrote:
Hi,
I have an older laptop. Not sure when I bought it. I'm thinking I bought it before 2009, however the CPU is an AMD 3300M which according to what I am reading was not in production until 2011. It has 4G of RAM and a 500GB HD. It's running Win7, which is a little slow.
I was thinking of replacing the HD with an SSD and potentially making it into a "Chromebook".... (Thunderbird/Libre Office/ Chrome Browser) I'm reading the SSD's are 10x faster than the HD. There has been prior discussions about breathing life into old hardware by replacing the HD with SSD and installing Linux (now we are on topic).
Initially I was thinking a small SSD since I will probably never use this laptop in production... But you never know. If these mods work out I might dual boot it - Win7 / Mint 17 KDE.
Newegg is selling a 240G Kingston SSD for $65 which is probably way more storage than I would ever need. http://www.newegg.com/Product/Product.aspx?Item=N82E16820721108
What type of lifespan should I expect for an SSD with moderate usage?
Anything specific I should be looking at?
Thank you so much for your help!!
--
Keith Smith
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A mouse trap, placed on top of your alarm clock, will prevent you from rolling over and going back to sleep after you hit the snooze button.
Stephen