Performance consistency tells us a lot about the architecture of these SSDs and how they handle internal fragmentation. The reason we do not have consistent IO latency with SSDs is because inevitably all controllers have to do some amount of defragmentation or garbage collection in order to continue operating at high speeds. When and how an SSD decides to run its defrag or cleanup routines directly impacts the user experience as inconsistent performance results in application slowdowns.
To test IO consistency, we fill a secure erased SSD with sequential data to ensure that all user accessible LBAs (Logical Block Addresses) have data associated with them. Next we kick off a 4KB random write workload across all LBAs at a queue depth of 32 using incompressible data. The test is run for just over half an hour and we record instantaneous IOPS every second.
We are also testing drives with added over-provisioning by limiting the LBA range. This gives us a look into the drive’s behavior with varying levels of empty space, which is frankly a more realistic approach for client workloads.
Each of the three graphs has its own purpose. The first one is of the whole duration of the test in log scale. The second and third one zoom into the beginning of steady-state operation (t=1400s) but on different scales: the second one uses log scale for easy comparison whereas the third one uses linear scale for better visualization of differences between drives. Click the dropdown selections below each graph to switch the source data.
For more detailed description of the test and why performance consistency matters, read our original Intel SSD DC S3700 article.
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25% Over-Provisioning
Performance consistency is not very good, but that was expected as we are dealing with a DRAM-less design. With insufficient cache for the NAND mapping table, it is very hard to manage the table efficiently in the steady-state environment, which results in decreased performance. The good news is that Chrome OS is extremely light and a scenario like this is basically impossible, so the data here is merely an interesting piece of information.
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TRIM Validation
To test TRIM, I filled the drive with sequential 128KB data and proceeded with a 30-minute random 4KB write (QD32) workload to put the drive into steady-state. After that I TRIM'ed the drive by issuing a quick format in Windows and ran HD Tach to produce the graph below.
It seems that TRIM is working, although there is an odd drop in read performance after the ~140GB mark.
Yeah, I'm typing this on mine running Arch on the default SSD. I can't see upgrading the HD when I really feel the ram is the bottleneck on the system. Enabling zram helps a little on the ram front and switching to BTRFS and enabling lzo got me back a bit of SSD space.
Out of curiosity, how much of your Google Drive space is full? I suspect, but haven't been able to confirm, that ChromeOS will cache some of your drive on the chromebook. It may be based on recent usage, or important/starred documents, but I suspect that's where the 'lost' space on the new SSD went.
By default, ext4 reserves 5% of the filesystem for root use (there's also also various options that can take up a few more percent of space like inode size/xattrs, extra superblocks, etc). So, there's ~10GB. I believe that chromeos also keeps a master copy of itself so the system can be reset (not sure where this is stored, however).
I have zero clue why chromebooks are so popular. I tried one and it was laughably basic compared to windows systems that are now pretty much priced the same. This might be ok, but for its simplicity, chrome doesn't really run any faster than its Windows counterparts, nor does it get much better battery life at all. I just see no reason unless you just absolutely detest windows 8.
Same reason iPad is. Simple machine for the crowd that wants to watch something and browse in one tab. PCs weren`t really made for this sector of the market anyway, function-wise or price-wise, so of course they went out.
Try, say, to open up a real spreadsheet on those and it`s a completely different picture of course.
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phoenix_rizzen - Tuesday, October 21, 2014 - link
Where's the 13th screw? I only count 12. Or is there one underneath the "warranty is void" sticker?Kristian Vättö - Tuesday, October 21, 2014 - link
Yeah, it's under the sticker. I.e. you have to break the sticker in order to take the bottom off, so there goes the warranty.phoenix_rizzen - Tuesday, October 21, 2014 - link
Ah. Sneaky bastards. :)DIYEyal - Tuesday, October 21, 2014 - link
I have the C720 running debian on a 128GB MyDigitalSSD and I'm pretty satisfied, the only complaint I have was the soldered RAM (can't upgrade to 4GB)quagga - Wednesday, October 22, 2014 - link
Yeah, I'm typing this on mine running Arch on the default SSD. I can't see upgrading the HD when I really feel the ram is the bottleneck on the system. Enabling zram helps a little on the ram front and switching to BTRFS and enabling lzo got me back a bit of SSD space.HeavensInMotion - Tuesday, October 21, 2014 - link
Out of curiosity, how much of your Google Drive space is full? I suspect, but haven't been able to confirm, that ChromeOS will cache some of your drive on the chromebook. It may be based on recent usage, or important/starred documents, but I suspect that's where the 'lost' space on the new SSD went.
tuxRoller - Wednesday, October 22, 2014 - link
By default, ext4 reserves 5% of the filesystem for root use (there's also also various options that can take up a few more percent of space like inode size/xattrs, extra superblocks, etc). So, there's ~10GB. I believe that chromeos also keeps a master copy of itself so the system can be reset (not sure where this is stored, however).tuxRoller - Wednesday, October 22, 2014 - link
Yeah, never mind. I see that you installed windows on this.You really need to make your test suite xplatform.
cylemmulo - Wednesday, October 22, 2014 - link
I have zero clue why chromebooks are so popular. I tried one and it was laughably basic compared to windows systems that are now pretty much priced the same. This might be ok, but for its simplicity, chrome doesn't really run any faster than its Windows counterparts, nor does it get much better battery life at all. I just see no reason unless you just absolutely detest windows 8.Michael Bay - Wednesday, October 22, 2014 - link
Same reason iPad is. Simple machine for the crowd that wants to watch something and browse in one tab. PCs weren`t really made for this sector of the market anyway, function-wise or price-wise, so of course they went out.Try, say, to open up a real spreadsheet on those and it`s a completely different picture of course.