Info SSD RAID Level Selection - Errr

[Robbie]

I presumed that this would be an easy forum question:

But I guess not!

Looking for the current thinking on SSD RAID levels. I've been running 5 SSDs in SHR-1 / BTRFS for quite some time and recently migrated them to a new NAS, giving me more drive bay options to play with.

Generally my risk level with RAID is low and I had long given-up on RAID5 / SHR1 for HDDs with RAID6 / SHR2 my bare minimum and even RAID10 when I needed it. Everything has a backup on spinning rust so data-loss is not hard concern, just the faff, stress, time and poor outcomes when re-silvering spinners.

SSDs brought RAID5 / SHR1 back from the dead as a viable option; I have been happy with it and the cold spare SSD has just gathered expensive dust. Googling around I could find very little advice for all-SSD arrays and what there is is a little old and the newish Synology RAID F1 thing does not apply to me. Aside from those who like to draw a false equivalence between HDD and SSD RAID levels the consensus a few years ago seemed* to be:

2x SSDs = RAID 1
3+ SSDs = RAID 5
8+ (ie 4 pairs) = RAID 10

* Understanding RAID 5 with SSD (Solid State Drives)
* Recommended RAID settings for HDD and SSD disks - StarWind Knowledge Base

Achieving a sufficiently IOPS was a real concern when I was spinning HDDs for my tasks but I have no idea what my required IOPS floor is these days as SSDs make it a complete non-issue for me. Currently I am network bottlenecked for sequential reads but not for writes (running about 70% or so of my 10 GbE link). If there is more sequential writes on the performance table somewhere I would take it but it isn't critical. I am not critical for SSD capacity but minded to blow the dust off the spare SSD to give me 6 populated bays.

- So is RAID 5 / SHR1 still the way to go for SSDs?
- Will adding a 6th SSD improve sequential writes or will there still be a parity writing bottleneck?
- Would dropping in a 6th drive as a hot spare be expensive overkill with backups close at hand?
- RAID 10 on SSDs looks really expensive and I don't need the IOPS and rebuilds are quick enough already but where does RAID 5 / SHR1 become risky?
- Am I overthinking this?

Ideas and thoughts welcome!

 

[Telos]

SHR/RAID5... unless you are doing serious number crunching, or are having 10GbE transfers, those SSDs are doing the work of a 5400rpm HDD... but more quietly.

Of course off-NAS backups go without saying... hmm... so, why did I mention that...

 

[Robbie]

I guess I take that as an SHR-1 recommendation?

The SSDs do work that only SSDs can do. All my other arrays are spinners, including off-NAS backups and archived HDDs.