On April 18, 2018 8:35:41 AM CDT, lsorense@csclub.uwaterloo.ca wrote:
I guess that would mean that scattering unused space on an SSD between the partions, means the controller probably sees it as being used. I left chunks allocated at the ends of the drives as recommended. I was just wondering if my stripes would increase that wear level capability, as well as providing for emergency recovery space(s).
Trying to guess how a drive does its wear leveling is impossible. Even if you are buying SSDs directly from the manufacturer and have a relationship with them, they usually won't tell you how it works.
Usually the drive has some extra space by design that it can use as a pool for writes, and then the old blocks are erased and put into the pool. If you use trim, you can add currently unused space in the filesystem to that free pool too. Some drives will occationally move data that never changes from blocks that have very few writes to blocks that are more work in the hopes that it will then be able to use those better blocks for more frequently changing data, but simpler drives may not do such housekeeping. There really isn't any way to know, unless they choose to advertise it. Of course it is likely a drive with a much higher promised number of write cycles likely is doing smarter housekeeping to keep block wear as even as possible.
I am not currently convinced that keeping unallocated space is worth it. Sure you make the free pool a bit larger, but you still end up writing the same amount of blocks and you make the usable size smaller. Having a larger free pool might help for systems that do a lot of writes since you are more likely to be able to have a free block to do a write, while the drive hasn't had time to erase the old blocks. On the other hand if you are doing enough writing that it could be a proble, maybe and SSD is the wrong type of drive to be using.
I have all my SSDs fully allocated and see no reason to do otherwise. Some people have some crazy theories that often have no facts behind them. They just assume the drive makers are dumb and haven't thought of this amazing problem that they just thought of. Of course some of the really cheap drives really are that dumb.
Thats what I tell people about my Phone. Its a smart phone. It just has a dumb operator. :-) I've always left bits of HDDs unalocated for emergency recovery installs. Live distros on usb make that provision unnecesary. Hugh also posted an interesting link to a page, I think it was on blkdiscard for thinly provisioned SSD's. Haven't gone there yet, but soon will. Thanks for your followup.
-- Len Sorensen
-- Russell