When Apple released OS X 10.10.4, alongside the offering came an implementation of Trim technology to clean up and potentially speed SSD write speeds over time. Users choosing to activate the feature, previously only on Apple-provided SSDs were greeted with a dire warning about the potential for data loss should the feature go bad in any way.
After a good first pass,
MacNN has concluded its second round of testing on a drive series thought to be problematic with the command -- the Samsung 840 and 850 drives, both in pro and EVO lines.
History
We covered what the Trim function is in the
previous article which launched this series. Up until the OS X 10.10.4 update, non-Apple drives had to rely on a sometimes dangerous hack to implement the cleanup feature. With 10.10.4 Apple has implemented a way to enable Trim for third-party SSDs, without resorting to the hacks. However, prior to executing the terminal command to turn the feature on,
Apple issues a stern warning, making it perfectly clear that the risk of data loss falls squarely in the hands of the user.
There are two types of Trim -- queued, and sequential. We're testing sequential Trim, as implemented by the drive's firmware.
Testing Gear
We've got four SSDs from Samsung for this round of testing: either old retail stock, or original firmware and in-use for some time. On the testing block are the 840 EVO and Pro, and the 850 EVO and Pro drives, all 2.5-inch size, and 512GB capacity. All of the drives are pre-loaded with 200GB of data, which isn't modified in any way by the testing process.
The testing hardware is a 2012 i7 Mac mini running OS X 10.10.4. Connected to the Mac mini to support the drives initially were a RocketStor 5212 Thunderbolt SATA dock, and a dual-channel USB 3.0 RocketStor 5122B dock. Even though we've been assured that the USB dock was passing Trim, we've shifted to a second RocketStor 5212 for this, and every future round of testing. All of the AC adapters for the hardware are connected to an uninterruptible power supply, to prevent power outages or brownouts from effecting the testing process or inducing any SSD failure.
Protocol
Transferred files vary in size from 64KB through 6.3GB, adding up to 250GB per transfer. The drive copies were set up "round robin," progressing through drives one through four, one copy at a time. When a copy option off the drive was completed, the data was deleted through a normal Finder move to trash and empty trash routine.
Drives sat completely idle between transfer rounds other than OS indexing, giving each drive as much time idle as both reading and writing, and more than enough time for Trim collection to begin between operations. At the conclusion of the test, each drive has seen over 800TB of data copied to the drive, and just as much read.
Limitations of the test
We're aware that the test isn't perfect. It is an accelerated process, where we're artificially loading and unloading the SSDs to implement the idle Trim feature faster than normal use. Our use pattern on the drives is far heavier than normal OS drive usage, and less sporadic -- a SSD with an installed OS is "tickled" a lot, for virtual memory, OS file access, app loading, and the like. What we're doing is more akin to constant use of the drive for a Photoshop scratch disk.
What this test is not is a comprehensive test of Trim's reliability under OS X and with all SSDs ever manufactured. Results for this round specifically apply only to the Samsung 840 and 850 Pro and EVO series. This test could have been performed under Windows as well, as the real issue here is the drive series' firmware routines, and less about any implementation by Apple.
Conclusions
We've now moved 800TB of data on and off each drive, across two separate firmwares per drive. For "normal" installations, that's right around eight years of extremely heavy system and application drive use. We are seeing some fairly significant cell failure quantities, but as the drives are over-provisioned, or more flash cells than required in the drive to hit the advertised capacity, so we're still at 100 percent storage capacity. The drives are still usable, but given how hard we've hit the drives, in an abundance of caution, we aren't going to use them for anything mission-critical anymore
So, we're not seeing any problems, and we've put years of use on the entire line in just a few weeks. We theorize that most of the complaints about drive corruption on the Linux side of the fence is more about queued Trim, which is not implemented in OS X. This isn't a guarantee, as it is a heavily time-compressed test, but we here at
MacNN feel safe about using the highly regarded Samsung offerings without qualm.
The Future
We're testing a few more drives round-robin right now. We've got a Crucial BX100 and a MX200, both in 512GB capacity on the rig. Additionally, an AMD Radeon 500GB and Patriot Blaze 480GB drive are running alongside the Crucial drives. We'll update this post in the future with the results of these four drives.