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I wonder what happens to SSD disk if I format it in Windows.

Does it replace old data with new data or tells it to erase data just like TRIM command without filling anything instead ?

I want to use SSD on my system that seems to not allow TRIM so I would just back up whole system, format and restore periodically to keep spare blocks on SSD to help longevity and speed.

I think this question applies also to formatting of USB flash drives and SDHC cards, I guess they need to be TRIMmed too if they use the same storage technology.

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    Windows does nothing related to TRIM before win7 / S2k8R2. Please specify what software you use.
    – Eroen
    Dec 11 '11 at 23:17
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Formatting a disk is not always equivalent to performing a manual TRIM on a drive - it depends if the format utility has explicit support for it. The Windows 7 format command does happen to have support for this. As for the difference between quick/full formats on Windows, if you do a quick format, it simply deletes the partition table and file listing. If you do a full format, it also does a full bad sector check (basically the same thing as a quick, format followed by running chkdsk /R on the new partition).

Does it replace old data with new data or tells it to erase data just like TRIM command without filling anything instead?

AFAIK, nothing is ever actually overwritten. I think the sectors are simply marked as free (unless you do a full format, which as overwrites each sector). Again, this is unless you're using an operating system with explicit TRIM support. From the blog post I linked to above:

Windows 7 requests the Trim operation for more than just file delete operations. The Trim operation is fully integrated with partition- and volume-level commands like Format and Delete, with file system commands relating to truncate and compression, and with the System Restore (aka Volume Snapshot) feature.

I expect that new builds of most Linux/Unix tools also have this support built-in, although you will need to verify this on a per-distribution basis (depending on TRIM support in the first place).

I want to use SSD on my system that seems to not allow TRIM so I would just back up whole system, format and restore periodically to keep spare blocks on SSD to help longevity and speed.

This usually will not suffice, as TRIM commands are far different from standard disk writes/reads/erase commands. If your operating system does not support automatically sending TRIM commands, you need to get a tool from your SSD manufacturer to manually TRIM the drive, or use another application like hdparam.


Final thoughts: If your operating system does not support TRIM, it would be wise to consider switching. While manually performing TRIM commands on the drive can increase the lifespan and performance of the drive (as opposed to simply doing nothing), using an operating system with explicit TRIM support will make these issues non-existent (and will make the drive last much longer than manually using a TRIM utility).

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  • I believe that all blocks are overwritten in a full format. (That is, it tests for bad blocks by overwriting them.) Dec 13 '11 at 23:58
  • @HarryJohnston good point, answer updated. Dec 14 '11 at 0:58
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    On Linux, tools like mkfs.ext4 or mkfs.f2fs don't overwrite all blocks manually, but they do attempt to discard the partition's contents via TRIM, before formatting it as ext4 or f2fs. (Partitioning tools such as fdisk do not.)
    – user1686
    Sep 4 '16 at 11:10
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Full formats DO NOT overwrite the data on the drive data area, only the filesystem control data is overwritten by a clean filesystem. Othwise unformat or recover accidentally formatted data could never work. Full Format just reads the remaining data area to verify the sectors can be read whereas quick format does not read-verify the data area.

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