I have a rocks cluster system with a NAS using a btrfs file system in a RAID 10 configuration. Recently we have been facing "no space left on device" errors that I have finally tracked down to metadata being almost entirely used up. So I wish to perform a balance operation to fix this issue.
What is not clear to me, is whether our users can continue working and accessing their directories on the nas while the balance operation is taking place? The manual on balance states:
"The on-disk state of the filesystem is always consistent so an unexpected interruption (eg. system crash, reboot) does not corrupt the filesystem. The progress of the balance operation is temporarily stored and will be resumed upon mount, unless the mount option skip_balance is specified."
Which makes me think that chunks of data only get reallocated after the balancing on that chunk is complete, but I haven't found a definite answer to my question anywhere: Is it safe for users to continue working, reading/writing data on the nas during a balancing operation, or is it necessary to take the system offline during this process that could take many hours or days for our TB's of data?