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
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  • Mr Perfect - Wednesday, March 18, 2009 - link

    "Needless to say, there was some definite fallout from that review. I’m used to negative manufacturer response after a GPU review, but I’m always a bit surprised when it happens in any other segment."

    Obviously you can't make a business out of irritating manufacturers, but when there really are issues, the readers want to know about them. After all, that's why we come here!
    Reply
  • gwolfman - Wednesday, March 18, 2009 - link

    You own Anand. Keep up the good work. I've seen you cited from many sites about the work you've done, in particular with SSDs. Best article I've read in months! Reply
  • Franco1 - Wednesday, March 18, 2009 - link

    I've been waiting a long time for this review. It was certainly worth the wait! I would love to see some benchmarks with 2+ drives in RAID configurations via onboard and add-on controller cards. Maybe another follow up? Reply
  • Howard - Wednesday, March 18, 2009 - link

    Looks like the Vertex is the drive to get, especially once the user base expands a bit. Reply
  • MagicalMule - Wednesday, March 18, 2009 - link

    Thanks for the article. Everyone is critiquing grammar and all this nonsense it seems, but I really enjoyed the article.

    It was very thorough and very informative.

    Keep up the good work. =).
    Reply
  • futrtrubl - Wednesday, March 18, 2009 - link

    You missed out a VERY significant step that causes the greater part of the slowdown associated with your scenario. After the block is read out to cache the block has to be erased before it can be written to again and as you pointed out earlier an erase cycle, and thus the entire read/modify+erase/write cycle, takes a relatively LONG time, much longer than a simple read/modify/write.

    Edward
    Reply
  • DrKlahn - Wednesday, March 18, 2009 - link

    I've worked in IT for 15 years and have played with very fast arrays and know a fair amount about storage. 2 months ago I replaced my Raptor boot/gaming drive with a GSkill Titan. In day to day use I have no stuttering. The only stutter I have seen was while installing a large patch, surfing with multiple windows/tabs open and using Outlook. It wasn't even a second. I did align the partition, turned off drive indexing and defragmentation, and turned on caching. In day to day use it simply kills the Raptor. Games and applications load in a fraction of the time. Vista boot time has decreased dramatically.

    This isn't a case of purchase justification. If the drive was a dud I would have moved it to a secondary machine, reinstalled the Raptor, and chalked it up as a bad decision. I simply have not run into any scenario in daily use that it performs worse than the drive it replaced and I have not seen any real stuttering in daily use.
    Reply
  • Gary Key - Wednesday, March 18, 2009 - link

    I have a GSkill Titan drive also and really like it. However, my experiences while positive overall, do not compare with yours when it comes to stuttering (yes, all optimizations have been done to the drive and OS). I still have significant stuttering problems when using multiple IM programs and having multiple windows/tabs open at the same time. I literally have to wait a few seconds when texting colleagues if more than two conversations are occurring at the same time as the system pauses, hitches, and stutters in this scenario. It is especially aggravating when on Skype and trying to text, speak, and transfer files at the same time. This does not occur on the Intel drive in my testing. Apparently, it is no longer a problem on the OCZ Vertex or Summit drives. Except for my example above, I would certainly use the Titan drive over my Raptor any day of the week. Reply
  • druc0017 - Wednesday, March 18, 2009 - link

    great article, keep up the good work, cant wait to see more updates, thx Reply
  • mikeblas - Wednesday, March 18, 2009 - link

    Is the Velociraptor really "World's fastest hard drive", as this article states? Faster than the Hitachi SAS drives? Reply

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