External SSD Questions

[benm]

Needing more disk space I bought a 960 Gb SSD. It's a Crucial M500. My question concerns how often I can write to the disk. I thought SSD's allowed 1,000 to 1,300 writes per memory location (for consumer models). But Crucial's website indicates it can write 72 Tb. The simple math seems to indicate that one could only write to each memory location 72 times. That doesn't seem right. Also, their website gives the 72 Tb figure for all of their SSDs including the 240 Gb version so now I am confused. Any SSD savants that can enlighten me? If it is helpful, I will be filling it about 40-45% right away and expect to add about 100 Gb per year thereafter. Thanks!

[RustBeltRaw]

You aren't the only one somewhat confused about write endurance. The Tech Report is currently testing a batch of solid-state drives to see how long they last, and if there are any performance degradations along the way. Results are interesting, and encouraging. So far, all of the drives they're testing have written 500TB (well in excess of all quoted endurance limits).

I am currently using SSDs in both of my laptops. A Corsair 120GB and an Intel 120GB. Neither has caused any trouble, but they're system drives, not backups. Much less write activity, so any opinion I could offer would be apples to oranges.

[Colin Southern]

Just get it and forget about it.

Case in point, I updated a laptop on a fishing boat to use an SSD about 18 months ago. Last week I ran the Intel SSD toolbox on it, and it estimated the life remaining to be ...

... 100%

(and that laptop is on 24x7)

We've been using Intel SSD drives for a couple of years now (ie dozens of them) - haven't had a single failure yet.

You wouldn't want to use them in servers, but in general PCs they're just fine.

[ajohnw]

The info that tends to be about isn't much use for estimating life and it's likely to relate to how it's used. It is also used in servers but the costs of that type are way way higher than what is generally being sold as ssd discs especially high capacity ones.

The only way to test write endurance is to fill them up completely, delete the lot which currently involved the use of trim and then do the entire thing again. As some include error recovery by storing additional parity information it's probably rather difficult to spot the early signs of failure. If they aren't filled up they will always preferentially write to the least used space. That's what they mean by wear levelling. The information enabling it to do that is also stored on the chips in them.

One other problem is that the technology keeps changing. It was all slc and now it's mlc. Slc just stores 0 or 1 in a cell, that's what it stands for single level cell. Mlc stands fo multi level cell. Initially this meant that a cell could store 0,1,2 or 3, in other words 2 bits.

Trim is a little bizarre. The os is effectively telling the ssd that it no longer needs certain blocks of data so that they can be erased for re use. The reason for this approach is that the cells must be erased to a clear state before now data can be written to them.

There is a fair amount of info about on the web on these subjects. There are also indications that people who use the storage available in them extensively are having to defragment them for the same reasons as early magnetic drive storage methods - files finish up all over the place. I suspect that is web myth though.

John
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[Manfred M]

There are also indications that people who use the storage available in them extensively are having to defragment them for the same reasons as early magnetic drive storage methods - files finish up all over the place. I suspect that is web myth though.

Definitely a web myth - a SSD has no moving parts, so fragmentation is never an issue. Fragmentation is only an issue where there is a physical read/ write head that has to move about between tracks, which is why fragmented files take longer to read. In fact the SSD onboard controller is used to ensure that the write function is spread out over the entire memory circuit.

[Colin Southern]

The info that tends to be about isn't much use for estimating life and it's likely to relate to how it's used. It is also used in servers but the costs of that type are way way higher than what is generally being sold as ssd discs especially high capacity ones.

For what it's worth, we got a quote the other day for a "server grade" one - 240GB; it was almost exactly TEN TIMES the cost of out usual 240GB PC SSD.

[ajohnw]

I don't trust the things yet so just use them for software mainly because I do not want my machine to break down and people have had that problem running windows on them,

Moving parts has nothing to do with it Manfred. It's the way data blocks are store and erased when no longer needed. New space can be all over the storage media in what ever size erase block the device uses. I suspect it is a myth as the system has no direct control over where data is stored on SSD. The wear levelling makes sure of that. Files are stored in multiple blocks and those may be all over the place.

John
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[benm]

Thanks everyone for the info. If any of you can recommend a good website that provides technical details on some of the intricacies of SSDs I would appreciate it. As an engineer my DNA compels me to find out how stuff works.

[RustBeltRaw]

If any of you can recommend a good website that provides technical details on some of the intricacies of SSDs I would appreciate it.

The Tech Report does an excellent job with testing and explanation of various SSDs. I recommend picking one that interests you, and looking up its review. They usually have very detailed comparisons with other drives on the market in each review.