Course 3, module 6.
In this module, we're going to talk about solid state drives, and
some of the ways they differ from the traditional spinning disks.
Solid state drives do not have cylinders or spindles or any moving parts at all.
They're made up of NAND flash memory chips, and you can see in the slide,
see the memory chips, we can see the power terminal and
the data terminal, this is a SATA connection.
Solid state drives cannot overwrite data like our spinning drives can,
so once something is marked as deleted, were sent to the recycle pan and
no longer in use, that area can't simply be overwritten.
That area must be white cleaned before it can be written to again.
And that's different than our traditional spinning disks.
Data is written to a solid state drives called pages, and
it's deleted in blocks, and blocks are made up of multiple pages.
We can think of pages like sectors and blocks like clusters.
It's not exactly the same, but it's a way to think about it.
So we're deleting data in multiple pages box.
Now, a lot of things happen with SSD solid state drives behind the scenes,
and this happens as soon as power is applied to the drive,
the user has no control on how this happens.
Some of the things that happen are wear leveling, trim and garbage collection.
Now, wear leveling, even it spreads out to write across the chips,
not to write to the same chip multiple times, because each of these chips has
a finite amount of writes that it's going to be able to do before it goes bad.
So by wear leveling, you increase the longevity of the drive itself.
Trim identifies the areas of the chips that are no longer in use and it wipes it.
This happens like I said behind the scenes, so
that's going to change where the area of data is stored.
Garbage collection actually reorganizes the data, putting files that
are no longer use or areas of the drives that are no more in use on one chip,
and taking files from areas that are still allocated,
that is still in use and moving them somewhere else on the drive itself.
So it's going to reorganize the data, and
then when that happens, trim comes through and wipes the chips.
So this can change theoretically, the hash value of your drive.
You just by applying power to it,
a write blocker won't stop this from happening, there's no way to stop it.
It happens as soon as power is applied to the disk.
So I just want you to be aware of that, and
that only applies to solid state drives.