How does VPCZ1's SSD GC work without TRIM?

You guys mentioned the drive's write performance can be recovered if leaving idle for a while....there are some kind of background GC builtin in the SSD...

If the OS does not tell the SSD drive which blocks can be erased.....
How does the drive able to find out which block can be recycled by the GC?

This is something only OS / Filesystem would know, right?

 

GC is managed by the SSD's firmware. So the OS has nothing to do with it. As the OS marks something as ''deleted'' the GC gets active when the pc is idle.

 

yes; I understand it

but VPC-Z1 (with SSD) owners are usually running the SSD in RAID-0 mode
so TRIM is not passed to the SSD; but there are claims that leaving the SSD idle could recover write speed so it is believed that some kind of GC is working internally.....I just wonder whether this is possible or not if OS does not tell SSD which blocks can be erased.....

how does the SSD GS knows which blocks to erase ??

 

I've heard of GC (it might even be Samsung...can't remember) that relies on some knowledge of the filesystem. This makes the most sense to me. It would be interesting to see if those who are running LINUX on their Zs see any performance degradation on a RAID-0 setup.

-Peter

 

They don't. A "delete" is simply asking the drive to change one or two blocks - the blocks that had information about the file. For all the drive knows, the blocks that contain the file data are in use, and no garbage collector can change that.

Only a couple of Samsung drives can do preemptive erases without TRIM, and they are to be avoided at all costs, because they make assumptions about the file system being NTFS in one particular version. Needless to say, that doesn't work with striped disks either.

The rest can not free up and pre-erase blocks for files that have been deleted, because there is no way for the drive to know. Only when a file is overwritten does the drive know that there are blocks to erase -- then it can map the old blocks as ready for erasure.

 

so the only thing SSD in Z1 can do is to pre-erase the extra spare blocks in the SSD?

e.g. 128G SSD probably actually contains 140G of physical blocks for wear levelling/GC/etc.

As the SSD knows which blocks are clean
whenever there is write operation, the drive should always perform the write to the clean blocks and mark the original blocks as invalid and will attempts to GC/clean those invalid blocks when idle, so in this case, freeing up at 12.8G at most

I guess this is how the idle GC works in Samsung Drive without TRIM and without NTFS knowledge in RAID mode as this can be done on drive level.

But the drive can free up 12.8G at most in the above case even only 1G of data is used by the filesystem
So the best is still to have TRIM support in RAID mode so if there is only 1G of data, all the blocks (127G + 12.8G) can be cleaned up by the GC

does it make sense?