How do I know if my writes are off my ZFS cache in ram?

[BoiDragon]

Hello! I have been trying to write a ton of data to my new server and I noticed that when I do so a lot of it is put in the ZFS write cache on my ram. I understand that this is normal but I am worried that If there were to be a blackout after I transfer files I would lose them in the ram cache. How do I know when all of the data is written to non-volitile disk?

Ryzen 5 2600
32 GB corsair vengence ram
Tuf gaming motherboard
5x 4tb ironwolf pro
EVGA 500 watt power supply

 

[jgreco]

Turn on sync writes to guarantee writes are committed to disk more quickly than the normal five second transaction group flush.

When that makes your writes very slow, look at adding a SLOG device (separate high speed log for the ZIL).

If you have no idea what I'm talking about, the ZIL/SLOG primer is over here:

Some insights into SLOG/ZIL with ZFS on FreeNAS

What is the ZIL? POSIX provides a facility for the system or an application to make sure that data requested to be written is actually committed to stable storage: a synchronous write request. Upon completion of a sync write request, the underlying filesystem is supposed to guarantee that a...

www.truenas.com

 

[BoiDragon]

Turn on sync writes to guarantee writes are committed to disk more quickly than the normal five second transaction group flush.

When that makes your writes very slow, look at adding a SLOG device (separate high speed log for the ZIL).

If you have no idea what I'm talking about, the ZIL/SLOG primer is over here:

https://www.truenas.com/community/threads/some-insights-into-slog-zil-with-zfs-on-freenas.13633/[

http://Thank you!

 

[jgreco]

http://Thank you!

That's cute. I forgot to circle around and say that my guess is that this isn't really a concern. ZFS will always have flushed your data out to disk after a handful of seconds, sync writes or async. The maximum amount of time this would normally take is maybe fifteen seconds. If you manage to catch it off-guard, it can be a bit more than that, but it is UNLIKELY.