XigmaNAS

Hi

I am new on NAS4Free, i migrated from FreeNAS 9.2.0. Sadly i had to create my zpool becauee importing failed due to the missing "space_histogram" feature flag in NAS4Free .

For my ESXi environment (ESXI 5.5) i created a zVol (blocksize standard -> 8KB) and exported the zVol via ISCSI.

When creating the zVol i used "sync=standard", but what is the standard value, to use sync writes or not to?

Can i change this afterwards (what i know is that i can insert/remove a SLOG via CLI):


zpool add zpool1 log /dev/ada4
zpool remove zpool1 /dev/ada4


Cheers
Thomy

Hi

I found the answer myself


zfs set sync=always zpool1/esx1
zfs set sync=standard zpool1/esx1 (default)

the option of disabled also exists, which means that zfs will ignore the sync that ESXi does for every single write. This is a big performance improvement if you don't need the guarantee that every write is written immediately. It doesn't cause corruption (per se) if there is a crash, instead it means that the ZFS server would go backwards in time if there is a crash. This is bad if the ESXi doesn't also crash simultaneously, because when the ZFS comes back up, you would then end up with some kind of corruption.

Hi

But what is now the difference between "standard" and "disabled", i don't get it

always = ZFS will sync every write to disk immediately, even if ESXi (or whatever app) doesn't ask for it.
standard = ZFS will sync writes when the app asks for it (ESXi always syncs, at least on NFS)
disabled = ZFS won't sync writes whether asked or not. In case of a crash, you will lose a few seconds of writes.

If you have an SSD SLOG, it will be used to sync the write.

ok