What kind of RAID? Motherboard-based? (couldn't tell from the description)? That is a problem if it is.
As for using USB disks, I don't think it's a bad idea necessarily, as long as you are verifying the backups and the speed/capacity are adequate for your purposes.
Our current tape backup solution has a dedicated server (using Microsoft DPM) that saves backups to a local hard drive, then rotates out the backups after a period of time to tape for longer term storage.
USB can be slow, but again, if it's meeting your needs then there's nothing fundamentally wrong with it. The thing to do is sit down and analyze your options and disaster recovery plans. How far back are you able to recover data? Are you able to recover from bare-metal failure? How long of a downtime would it be? Are your backups taking too much time to perform or hindering server performance while users are trying to get work done?
Also, how available is the data? Tapes are high-capacity and easier to store for a period of time, but if you need data on a tape that your drive no longer reads or can't get new tapes for your device because it's too old, what then? Hard drive backup tends not to have this issue, as there are tapes that you can have trouble reading from ten years ago but USB will be around and usable for quite some time in all likelihood.
And is your solution proprietary? I.e., the old unix tarballs from way back when dragons were real and pirates didn't have law degrees can still be decompressed and read. If your backup is in a format specific to a product, do you think you can recover data if the program is no longer supported or has other issues?
What it boils down to is analyzing your situation and coming up with recovery scenarios and making sure you're covered in the most likely events. USB drives are fine, as long as they meet your needs. But they also can be prone to any other hardware failure, so you should probably make sure to cycle them out periodically for redundancy.
Let's try to reply one question at a time:
- Is TRIM support necessary for modern (2015-2016 era) SSDs?
Short answer: in most cases, no. Long answer: if you reserve sufficient spare space (~20%), even consumer-grade drive usually have quite good performance consistency values (but you need to avoid the drives which, instead, choke on sustained writes). Enterprise-grade drives are even better, both because they have higher spare space by default and because their controller/firmware combo is optimized toward continuous use of the drive. For example, take a look at the S3700 drive you referenced: even without trimming, it has very good write consistency.
- Often drives are advertised as having improved built-in
garbage-collection, does that obviate the need for TRIM? How does
their GC process work in RAID environments
The drive garbage collector does its magic inside the drive sandbox - it does not know anything about the outside environment. This means that it is (mostly) unaffected by the RAID level of the array. That said, some RAID levels (the parity-based one, basically) can sometimes (and in some specific implementation) increase the write amplification factor, so this in turn means higher work for the GC routines.
- A lot of articles and discussion from earlier years concerns SLC vs
MLC flash and that SLC is preferable, due to its much longer lifespan, however it seems all SSDs (regardless of where they sit on the Consumer-to-Enterprise spectrum) are MLC thesedays - is this
distinction of relevance anymore
SLC drives have basically disappeared from the enterprise, being relegated mainly to military and some industrial tasks. The enterprise marked is now divided in three grades:
- HMLC/MLCe flash is the one with the better binned MLC chips, and certified to sustain at least 25000/30000 rewrite cycles;
- 3D MLC chips are rated at about 5000-10000 rewrite cycles;
- normal planar MLC and 3D TLC chips are rated at about 3000 rewrite cycles.
In reality, any of the above flash types should provide you with plenty of total write capacity and, in fact, you can find enterprise drives with all of the above flash types.
The real differentiation between enterprise and consumer drives are:
- the controller/firmware combo, with enterprise drives much harder to die due to unexpected controller bug;
- the power-protected write cache, extremely important to prevent corruptions to the Flash Translation Layer (FTL), which is stored on the flash itself.
Enterprise grade drivers are better mostly due to their controllers and power capacitors, rather than due to better flash.
- Enterprise SSDs tend to have have much higher endurance /
write-limits (often measured in how many times you can completely
overwrite the drive in a day, throughout a drive's expected 5 year
lifespan), does this obviate any concerns over Write-Amplification
caused by not running TRIM?
As stated above, enterprise grade drives have much higher default spare space (~20%) which, in turn, drastically lowers the need for regular TRIMs
Anyway, as a side note, please consider some software RAIDs that support TRIMs (someone said Linux MDRAID?)
Best Answer
You mean if the disk is damaged such that corrupted data is read off it that appears legitimate? That's not a "normal failure". RAID 1 protects against normal failures of a single disk.
It also won't protect you if one disk catches on fire and blows up the other one. These are "abnormal failures". For example, if one disk's write hardware breaks and it doesn't really write data but doesn't report errors, then RAID 1 will fail.
Modern disks have data error detection. So unless there's something like a firmware bug, if data cannot be read accurately, the disk should be able to report it.
An inconsistency between two disks in a functioning RAID 1 array is already a failed condition caused by something outside what the RAID 1 array protects against. For example, it could occur if power is removed. But RAID 1 is not supposed to protect you against power loss. So it doesn't matter if it corrupts data in that case -- it's not supposed to not do that. Whichever disk it copies is fine. It doesn't matter. Neither is more correct than the other.
RAID 1 makes sense if you want to protect against the failure of one device. Write endurance has nothing to do with anything. A RAID 1 array will fail if either device cannot be written to.
RAID is not backup. RAID only gives you the ability to tolerate a specific category of faults. If your fault is not one of those in that specific category, RAID won't help you and can even hurt you.