NVMe parallel writes

Question

I'm trying to understand better how writing to NVMe can be optimized.

I have a process which writes a large amount of data to disk (~100 gb) in one batch job. The data is spread across 100s of files.

I have multiple NVMe disks available and will be writing separate files in parallel in one process using multiple threads (~10).

Currently all the data is written to a single NVMe disk, I am wondering if a potential performance improvement could be achieved by writing the data across multiple disks in parallel or if a single NVMe device can handle parallel writes on it's own?

Appreciate any input

Are the files written over multiple different directories? Are they compressible? — shodanshok, Mar 04 '22 at 09:44
The files are written over multiple directories and are already compressed — R.Smith, Mar 04 '22 at 11:27

score 1 · Answer 1 · answered Mar 04 '22 at 09:39

Well certainly the NVMe spec allows for something like 64k queues, each can contain 64k entries - so the spec itself allows for some very high-end concurrency operations - whether or not the actual drive supports that many is a different thing but certainly they'll support hundreds of queues and hundreds of queue entries. All of this will help.

That said the instinct is that more drives will be better but it really does depend on how flooded the PCIe/PCH is - if there's lots of little writes then there's a chance that the bus isn't fully busy so smearing across multiple disks may help a little, but if it's fully utilised, as you'd likely see in large sequential writes, then a single disk could be as quick as multiple disks.

Of course this is all before you consider things like RAID 1/10 or 0 and the impact that would have - you ideally want something like that for resilience.

Ultimately you should test this, that's the proper answer but it depends how many drives and how much time you have to do the testing - but that's the only way to truly know.

NVMe parallel writes

1 Answers1