The Trim Command: Coming Soon to a Drive Near You

We run into these problems primarily because the drive doesn’t know when a file is deleted, only when one is overwritten. Thus we lose performance when we go to write a new file at the expense of maintaining lightning quick deletion speeds. The latter doesn’t really matter though, now does it?

There’s a command you may have heard of called TRIM. The command would require proper OS and drive support, but with it you could effectively let the OS tell the SSD to wipe invalid pages before they are overwritten.

The process works like this:

First, a TRIM-supporting OS (e.g. Windows 7 will support TRIM at some point) queries the hard drive for its rotational speed. If the drive responds by saying 0, the OS knows it’s a SSD and turns off features like defrag. It also enables the use of the TRIM command.

When you delete a file, the OS sends a trim command for the LBAs covered by the file to the SSD controller. The controller will then copy the block to cache, wipe the deleted pages, and write the new block with freshly cleaned pages to the drive.

Now when you go to write a file to that block you’ve got empty pages to write to and your write performance will be closer to what it should be.

In our example from earlier, here’s what would happen if our OS and drive supported TRIM:

Our user saves his 4KB text file, which gets put in a new page on a fresh drive. No differences here.

Next was a 8KB JPEG. Two pages allocated; again, no differences.

The third step was deleting the original 4KB text file. Since our drive now supports TRIM, when this deletion request comes down the drive will actually read the entire block, remove the first LBA and write the new block back to the flash:


The TRIM command forces the block to be cleaned before our final write. There's additional overhead but it happens after a delete and not during a critical write.

Our drive is now at 40% capacity, just like the OS thinks it is. When our user goes to save his 12KB JPEG, the write goes at full speed. Problem solved. Well, sorta.

While the TRIM command will alleviate the problem, it won’t eliminate it. The TRIM command can’t be invoked when you’re simply overwriting a file, for example when you save changes to a document. In those situations you’ll still have to pay the performance penalty.

Every controller manufacturer I’ve talked to intends on supporting TRIM whenever there’s an OS that takes advantage of it. The big unknown is whether or not current drives will be firmware-upgradeable to supporting TRIM as no manufacturer has a clear firmware upgrade strategy at this point.

I expect that whenever Windows 7 supports TRIM we’ll see a new generation of drives with support for the command. Whether or not existing drives will be upgraded remains to be seen, but I’d highly encourage it.

To the manufacturers making these drives: your customers buying them today at exorbitant prices deserve your utmost support. If it’s possible to enable TRIM on existing hardware, you owe it to them to offer the upgrade. Their gratitude would most likely be expressed by continuing to purchase SSDs and encouraging others to do so as well. Upset them, and you’ll simply be delaying the migration to solid state storage.

Free Space to the Rescue Restoring Your Drive to Peak Performance
POST A COMMENT

236 Comments

View All Comments

  • VaultDweller - Wednesday, March 18, 2009 - link

    I love it when people critique someone's critique of grammar... and get it wrong.

    It's an SSD, not a SSD.
    Reply
  • gwolfman - Wednesday, March 18, 2009 - link

    lolz Reply
  • sidex - Wednesday, March 18, 2009 - link

    I would like to know the firmware version of Vertex used in your review. To me sounds the old 0112 Reply
  • kensiko - Wednesday, March 18, 2009 - link

    Yes that is important to know.

    I'm sure this is not done with the latest firmware available which is 1199. This version got better performance.

    Firmware 1275 is coming also.

    Anand, will you update your benchmarks with the latest firmware?

    If not, then the benchmarks are obsolete.
    Reply
  • Anand Lal Shimpi - Wednesday, March 18, 2009 - link

    I tested with the shipping firmware for this article (0122). I've been playing around with 1199 in the lab and will most likely have an update in a couple of weeks once I've done a thorough evaluation of it. By then I should also have the final version of the new Samsung drive and maybe even some other interesting things.

    For now, I've got to get to work on the new Mac Pro and the updated Ion article :) I need a small break from SSDs por favor :)

    Take care,
    Anand
    Reply
  • VaultDweller - Wednesday, March 18, 2009 - link

    Awww, don't you have some underlings to do your SSD-related will?

    Would love to see an update, and would love to see Corsair's SSD drive tested as well (it's based on Samsung's last generation MLC controller, and doesn't seem to emphasize sequential like the Summit does).
    Reply
  • Anand Lal Shimpi - Wednesday, March 18, 2009 - link

    I will do an update on the new firmware, I just want to do it right so it'll take some time :)

    I'll put in a request for the Corsair drive as well :)

    -A
    Reply
  • Slash3 - Wednesday, March 18, 2009 - link

    Page 29: "Not all applications will launch faster than a VelociRaptor on a SSD, but let's not forget that the VelociRaptor is the world's fastest hard drive."

    Really? What about the nice and speedy enterprise-level 15k SAS/SCSI drives everyone neglects to acknowledge? :)
    Reply
  • George Powell - Wednesday, March 18, 2009 - link

    I believe it refers to consumer drives. While SAS drives are beginning to be a possibility on the desktop with newer motherboards supporting them natively, the drives themselves are too expensive and too noisy for most consumers to actually want them.


    Reply
  • FishTankX - Wednesday, March 18, 2009 - link

    Good info. However, I noticed one mistake.

    Second page
    Samsung had a MLC controller at the time but it was too expensive than what SuperTalent was shooting for.
    Reply

Log in

Don't have an account? Sign up now