@biggen said in RAID5 SSD Performance Expectations:
@Pete-S said in RAID5 SSD Performance Expectations:
@Pete-S said in RAID5 SSD Performance Expectations:
@scottalanmiller said in RAID5 SSD Performance Expectations:
@Pete-S said in RAID5 SSD Performance Expectations:
Having a drive failure will become such an odd failure like having a raid controller, a motherboard or a CPU fail. You'd just replace it and restore the entire thing from backup.
I think drives already fail less than RAID controllers. From working in giant environmnts, the thing that fails more than mobos or CPUs is RAM. That's the worst one as it does the most damage and is hard to mitigate.
The difference though is that mobo, controllers, PSUs, are stateless to the system but drives are stateful. So their failure has a different type of impact, regardless of frequency.
Well, the stateful-ness of the drives is not something we can count fully on, hence the saying "raid is not backup".
What I'm proposing is that when it becomes very unlikely that a drive fails we could rethink our strategy and go for single drives instead of raid arrays. In the very unlikely event that a failure did occur, we are restoring from backup, which we are prepared to do anyway.
With HDDs the failure rate is too high but with enterprise SSDs it's starting to get into the "will not fail" category.
As an example assume we have 4 servers with a RAID10 array of 4 x 2TB drives each. Annual failure rate of HDDs are a few percent, say 3% for arguments sake. With 16 drives in total, every year there is about 50% chance that a drive will fail. So over the lifespan of the servers it's very likely that we will see one or more drive failures.
Now assume the same 4 servers with a single enterprise 4TB NVMe drive in each. Annual failure rate is 0.4% (actual number a few years back). With 4 drives in total, every year there is less than 2% chance that any drive will fail. So over the lifespan of the server it's very unlikely that we will ever see a drive failure at all. Sure, if it does happen anyway, we are restoring from backup instead of rebuilding the array.
As long as you can justify the downtime in the event that a single drive failure takes an entire server down (albeit with a low statistical chance).
If that isn't a concern no use running RAID anyway.
That makes sense. But regardless of RAID or not, there are always things that can take the entire server down, for instance a motherboard failure. So that is something that is always there.
I think you can take the probability x downtime to get the average downtime. And that times the cost per hour if you want to put it in $$$.
So if something is 2% likely to happen and causes 10 hours of downtime, you get 0.2 hours (12 minutes) of downtime on average. If that downtime is going to cost $10K per hour then it's $2K.
If that downtime is unacceptable you need to have more servers or more reliable servers. 12 minutes of downtime per year is 99.997% availability. 10 hours of downtime per year is 99.8%.
