Upgrading the SSD in Chromebook & MyDigitalSSD Super Boot Drive M.2 2242 SSD Review
by Kristian Vättö on October 21, 2014 8:00 AM ESTRandom Read/Write Speed
The four corners of SSD performance are as follows: random read, random write, sequential read and sequential write speed. Random accesses are generally small in size, while sequential accesses tend to be larger and thus we have the four Iometer tests we use in all of our reviews.
Our first test writes 4KB in a completely random pattern over an 8GB space of the drive to simulate the sort of random access that you'd see on an OS drive (even this is more stressful than a normal desktop user would see). We perform three concurrent IOs and run the test for 3 minutes. The results reported are in average MB/s over the entire time.
Surprisingly the 16GB Kingston M.2 drive has excellent random read performance. I suspect that having such little NAND helps with random read performance because you are practically hitting the same LBAs, so some IOs may be cached and there is less tracking overhead as well. The MyDigitalSSD drive, on the other hand, does not fare that well, although random read performance has never been the biggest strength of Phison controllers in my experience.
Both the MyDigitalSSD and Kingston drives have rather poor random write performance. Since neither of the drives have a DRAM cache, the host IOs along with the NAND mapping table need to be cached in the internal cache of the controller (or alternatively in NAND), which adds limitations since the internal SRAM caches are typically only a few megabytes in size and NAND is much slower than DRAM.
Sequential Read/Write Speed
To measure sequential performance we run a 1 minute long 128KB sequential test over the entire span of the drive at a queue depth of 1. The results reported are in average MB/s over the entire test length.
Sequential read is also better on the 16GB Kingston drive, so it seems that the additional NAND adds quite a lot of overhead when there is no DRAM for caching purposes. In write speed the MyDigitalSSD drive is considerably faster, although 2.5" 256GB drives are also substantially faster still.
AS-SSD Incompressible Sequential Read/Write Performance
The AS-SSD sequential benchmark uses incompressible data for all of its transfers. The result is a pretty big reduction in sequential write speed on SandForce based controllers, but most other controllers are unaffected.
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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.