ZFS high cpu load with low io and cpu usage

[bibin]

Hi,

We are using zfs on one of our servers. Both deduplication and compression features of zfs are also enabled in it. We were trying to migrate a vps disk from an ext4 server using 'DD', but the migration process seems to be resulted in an increased load on zfs server and hence the migration couldn't able to complete. The load issue is fixed by rebooting the zfs server. We have a powerful CPU with 32 cores on zfs server. Didn't find anything helpful from 'iotop' and 'top' commands outputs. It seems like all the 32 cores are not functioning during the migration process. Please help us.

Thank You !

 

[unwind-protect]

If you are migrating off the ZFS, why not put it into readonly and turn off dedup for the period?

 

[bibin]

I think if we have set deduplication after the data writes, existing data will not be changed. You are saying to set the readonly for the zpool dataset. Will it works if we set deduplication after the migration?. Also if ZFS dataset is set to readonly, then how deduplication is able to work?

 

[unwind-protect]

The way I understood what you are doing is that you move the data off ZFS. So you wouldn't need to write to it. Obviously once the filesystem is readonly you wouldn't have to worry about dedup one way or another.

 

[bibin]

Hi,

We are trying to migrate to zvol disk from a ext4 system. If we set readonly for zvol dataset, then how a data write(migration) will happen?. Can you clarify this for us? Appreciate your help.

Thank You !

 

[unwind-protect]

What I am saying is that I needed clarification. So you want to move to ZFS, not away from it?

 

[bibin]

Yes.

 

[unwind-protect]

OK.

Are you able to post a top(1) output while this is going on?

We need more details such as how much memory there is, how much CPU and what "high load" means, specifically.