Plextor M5M (256GB) mSATA Review
by Kristian Vättö on April 17, 2013 10:20 AM ESTTRIM Performance
Plextor calls their garbage collection "True Speed". They are quite heavily advertising the dirty state performance of their SSDs, although I have to say that I haven't found their SSDs to be anything special in this regard. As we already found out in the performance consistency test, Plextor relies heavily on idle garbage collection: When the drive has no other tasks to complete, it will start cleaning up itself.
For starters, I ran a secure erased M5M through HD Tach to get the baseline performance:
As usual, I followed up by filling the drive with sequential data and then hammered the drive with 4KB random writes (QD=32) across all user-accessible LBAs for 60 minutes. I then ran HD Tach to graph the data:
Performance does get pretty bad, but that was expected given the performance consistency (the lower the random write speed is after torture, the worse the HD Tach graph looks). Next I TRIM'ed all user-accessible LBAs and reran HD Tach to make sure TRIM work as it should:
And it does.
Facebook
Twitter
RSS
36 Comments
View All Comments
JPForums - Thursday, April 18, 2013 - link
Sorry, I wasn't trying to bait you. The posts just came off as a little hostile. Probably a result of the my morning meetings.If I'm understanding you correctly, your biggest issue is with the method of consistency. I read in another of your posts that this method is similar to the tests that several large enterprises use. You seem to be familiar with these methods. Is there an alternate (better) method in use that Anandtech could be using? Alternately do you have a superior method in mind that isn't currently in use? I'm guessing (for starters) you'd be happier with a method that measures individual operation latencies (I would too), but I'm unaware any tools that could accomplish this.
JellyRoll - Thursday, April 18, 2013 - link
The consistency testing and all trace based testing used by this site are tested without partitions or filesystems, and no TRIM functionality. This has been disclosed by the staff in the comment sections of previous reviews.If you are testing consumer hardware, the first order of the day is to use methods that accurately reflect real workloads. Removing the must crucial component required for performance consistency (TRIM), then testing 'consistency' anyway, is ridiculous. Would you test a vehicle without fuel?
Kristian Vättö - Thursday, April 18, 2013 - link
TRIM does not affect performance consistency of a continuous write workload. TRIM will only tell the controller which LBAs are no longer in use - the actual LBAs still need to be erased before new data can be written. When you're constantly writing to the drive, it doesn't have time to erase the blocks as fast as new write requests come in, which causes the performance to sink.If you know methods that "accurately reflect real workloads" then please share them. Pointing out flaws is easy but unhelpful unless you can provide a method that's better.
JellyRoll - Thursday, April 18, 2013 - link
Pasted from the Wiki:"The TRIM command is designed to enable the operating system to notify the SSD which pages no longer contain valid data due to erases either by the user or operating system itself. During a delete operation, the OS will both mark the sectors as free for new data and send a TRIM command to the SSD to be marked as no longer valid. After that the SSD knows not to relocate data from the affected LBAs during garbage collection."
During a pure write workload there is no need for the SSD's internal garbage collection functions to read-write-modify in order to write new data. That is the purpose of TRIM. Without TRIM writes require read-write-modify activity, with TRIM they do not. Very easy to see how it boosts performance.
Kristian Vättö - Thursday, April 18, 2013 - link
You still have to erase the blocks, which is the time consuming part. Again, there's no time for normal idle garbage collection to kick in. Yes, the drive will know what LBAs are no longer in use but it still has to erase the blocks containing those LBAs. If you let the drive idle, then it will have time to reorganize the data so that there'll be enough empty blocks to maintain good performance but that is not the case in a continuous write workload.JellyRoll - Thursday, April 18, 2013 - link
It is removing the 'write' from the read-write-modify cycle. Writing a page smaller than the block requires the SSD to relocate the other data in the block first, adding work for the SSD. Remember, they erase at block level. If it isn't aware that the rest of the block is also invalid (the point of TRIM) it must first move the other data.Kristian Vättö - Thursday, April 18, 2013 - link
It's read-modify-write cycle (read the block to cache, modify the data, write the modified data) so the write operation is still there, otherwise the drive wouldn't complete the write request in the first place. You also seem to be assuming that the rest of the pages in the block are invalid, which is unlikely the case unless we're dealing with an empty drive. Hence it's exactly the same cycle with TRIM as you still have to read at least some of the data and then rewrite it. You may have to read/write less data as some of it will be invalid, but remember that garbage collection (with TRIM off) will also mark pages as invalid on its own. That's the reason why performance will stay high even if TRIM is not supported (e.g. OS X), assuming that the garbage collection is effective (there's at least 7% OP so there is always invalid pages).JellyRoll - Thursday, April 18, 2013 - link
I am not assuming the data is still valid, the SSD does. It has to move the data if it considers it valid. TRIM removes the need to move this 'other' data, thus speeding the drive.Kristian Vättö - Monday, April 22, 2013 - link
Here are some tests I did with Plextor M5 Pro XtremeRAW (no partition): https://dl.dropboxusercontent.com/u/128928769/Cons...
NTFS (default cluster size): https://dl.dropboxusercontent.com/u/128928769/Cons...
As you can see, there's no major difference. In fact, there's a bigger slowdown with NTFS versus raw drive.
JPForums - Thursday, April 18, 2013 - link
1) I was not aware that another website created this method of characterizing performance, but I'll give you the benefit of the doubt. Nonetheless, the statement that Anand introduced it to the standard test suite here at Anandtech in the Intel SSD DC S3700 review is a true statement. Given the context of the original statement, this is more likely the intended interpretation. Out of curiosity, which site did create the method?2) I'm not sure whether or not the test measures individual operation latencies or not as IOPS is basically the inverse of an average of the those latencies over time. It is kind of like the difference between FPS and Frame latencies. That said, the representation on the graphs is more the inverse of a one second sliding window average. Saying as much is kind of a mouthful, though. How would you phrase it?