How do you TRIM unallocated/unformatted space after partition shrinking on an SSD in Windows?

Question

How do you TRIM completely unused, unallocated, unformatted, unpartitioned space (but other volumes still exist) on an SSD in Windows 11, that used to contain data, for over provisioning? (For note: when I say "empty space" I mean space that is now unallocated, unformatted, etc., not necessarily unused space in an existing volume/partition.)

I've looked around and found a lot of answers for people asking similar questions about "empty space" that never contained anything (such as on a new drive), so a TRIM is unnecessary, and that's understandable. However, I used to have my entire SSD partitioned and formatted and had regularly nearly filled it up (certainly more than the unused space I'm trying to over provision now) and only recently realized there are many benefits to over provisioning that outweigh the loss of storage space. I didn't do a TRIM before shrinking the partition however, so the SSD may think there is still data in that now "empty space".

I am under the assumption that TRIMing a volume (C, D, etc.) only applies to the "space" (sectors/blocks, whatever) that volume occupies (or could potentially occupy, including its unused space), but does not TRIM outside that volume (presumably so it's not TRIMing space that only Windows doesn't know about).

So, if I want to be sure that the SSD firmware knows that space is available for over provisioning, how can I be sure it knows? Is there a command or tool to tell the SSD firmware specifically that it's for over provisioning, or how can I TRIM that "empty space" (that used to be used) outside any volumes?

If there is not a command or tool to TRIM the "empty space", would just creating a new partition/volume in the space I want for over provisioning, TRIMing that, and deleting it effectively do what I want?

Answer 1

Unformatted space, like what you see when you shrink your partition, is separate from overprovisioned capacity. The OS cannot see overprovisioned areas, and the SSD will not automatically use unformatted (shrunk) space for overprovision tasks.

Some manufacturers do have tools to adjust the amount of space used for OP, like Samsung Magician for their SSDs. Each manufacturer sets aside a different amount of OP space on the disk (usually 5-10%) that you never see. You do not need to add more space to it.

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SSD TRIM has no purpose on unformatted areas of your disk

Answer 2

I think what OP means to do is reserve for example 10% of LBA space and not do anything with it so the drive can use it for overprovisioning. By making certain this area is trimmed you'd be certain this piece of LAB space isn't mapped to any physical NAND real-estate. If you then refrain from writing data to this area, the LBA space remains un-mapped.

I do data recovery and have observed:

• Deleting a partition using Disk Management does not trigger TRIM, IOW data remains recoverable (demonstration).
• Creation of a new partition + new file system in this unallocated space triggers TRIM for this area (IOW the LBA range is un-mapped). This is as OP assumes, vital because before the firmware can use this space as it pleases it has to be made aware of this. TRIM is the command to communicate this to the controller/firmware. If you want to use this space purely for overprovisioning it may be a good idea to then simply delete the partition again.

Over-provisioned space is simply a percentage of NAND real-estate that isn't mapped to LBA. It does not matter whether this space is maintained at firmware level, by means of some sort of HPA area (this is basically what manufacturer tools that offer an over-provisioning configuration option do) or that it's set aside by the user for this purpose. The only difference is that the latter does not hide the area like HPA (host protected area) for example does. However, by leaving/making the space unallocated after you have it trimmed, you prevent from new data being written to it.

Alternatively, you can set a HPA area (on a still unused or empty drive) using for example hdparm. It's essentially the same idea: Any region of the SSD that's not mapped to LBA will act as overprovisioned space.

You can not count on writing zeros to the area. Although trimmed LBA space usually returns zeros when you read from it, this is purely the firmware simply returning zeros since it detects user is trying to read from un-mapped LBA. This is different than actually writing zeros (although on modern SSDs firmware may detect zeros and not actually allocate physical NAND to store these, but this is a different topic).

Any overprovisioning will contribute to for example prolonging SSD life time. One manufacturer trick to offer higher quality SSDs with for example increased endurance, is simply increasing over-provisioned space at firmware level.

Answer 3

If I had to do it, I would boot a Linux LiveUSB, create an empty partition there, blkdiscard it, then remove the partition. This is the most direct way to do exactly what you want. But if you're not very familiar with Linux partitioning tools, then there's a high chance you can destroy something else instead, so I wouldn't recommend this as the go-to method for everyone.

The next best option is what Joep van Steen suggested: create a new partition, "QUICK"-FORMAT IT AS NTFS, then delete the partition. You'll have the NTFS metadata written there, but it's most likely very little compared to what you have there now.

I can not be completely sure that Windows does not TRIM an empty partition upon creation, or that it does not TRIM other filesystems. But it is highly likely that it doesn't, and it most certainly does TRIM NTFS before formatting it.

Answer 4

An SSD is less vulnerable to reading unallocated disk areas, with a good chance that doing so will retrieve only zeros.

If you worry about the data that was previously on this space, and would like to take no chances, I can see two solutions:

• Get a disk editor product and zero out the unoccupied space. This is unsafe since you would need to calculate sector offsets and a mistake could be costly.

• Create a partition over the unoccupied space and zero out the partition with some utility, or copy to it one or several large files that will terminate with an insufficient space message. Deleting the written files, once they fill out the partition, will certainly do the TRIM

The second option is much more practical.