Hi,

I would like to ask you to make me clear two things about SSDs.

1) Very often, when reading about the subject, there is an advice to leave some free space on the SSD.
I would like to ask, what does it mean?
How does one leave free space on a disk?
If I partition the disk, leaving unpartitioned area somewhere at the end, will the disk controller actually understand that?

And most importantly, does it matter at all for modern disks?

2) Can bad thing happen if fstrim is interrupted during operation (e.g. system shutdown while fstrim was scheduled to run by cron)?

Thanks in advance!

My SSDs are:
- Samsung SSD 850 EVO M.2 250GB, EMT21B6Q, max UDMA/133
- Samsung SSD 850 PRO 256GB, EXM02B6Q, max UDMA/133

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Best regards,
Andrzej Telszewski

I'll give you my opinions on this; others may have a different view.
I believe this advice only applies to older SSDs. It refers to leaving some unallocated space(i.e. unpartitioned space) on the drive rather than partitioning the entire drive. This unallocated space can be used by the SSD firmware controller to increase the efficiency and life of the drive by using the unallocated space to perform certain functions peculiar to SSD drive maintenance, namely wear leveling, garbage collection and dealing with a technical phenomena known as write amplification:

https://en.wikipedia.org/wiki/Write_...r-provisioning

The practice is known as "over-provisioning". I believe most modern SSDs, and certainly your Samsung SSDs, already come from the factory with hidden space not seen by your bios or operating system to be used for this purpose, i.e. they come from the factory over-provisioned. That was not always true of early SSDs. You can certainly leave some unallocated space on your SSDs if you want and it will be added to your already provided over-provisioned space and automatically used by your SSD firmware controller as needed. It may even be useful to do so in certain situations. In practice, I haven't found it necessary on recent SSD drives from Samsung or Intel. I don't have experience with other manufacturers.

As I understand it, fstrim just clears unused blocks from an SSD drive. If fstrim is interrupted, I would assume it just wouldn't complete the "trimming" of unused blocks and the next time fstrim was run those blocks would be detected and cleared.

Hi,

OK, I'm going to believe it too and won't bother any more. Thanks ;-)

This sounds safe.

Thanks.

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Best regards,
Andrzej Telszewski