iSCSI using the whole raid

[roundrobinknowledge]

system specs
10x 1tb 2.5 inch spinning disk
4x 1tb SSD
128 GB ram
2x xeon processors
supermicro board and chassis

right now I have the 10 spinning disks as 2 raidz2 put together. I have a zvol extent shared out by iscsi on this pool.
the 4 SSD I haven't setup yet and was thinking either raid10 or another raidz2. I would like to some how use all of the SSD space on a new iscsi share.

What I am wonder is if it possible\safe to share the whole pool. Every where I looked says if I go over 80% disk space I will inure a performance plenty and other bad things will happen.

I also Have a second questions, right now there is 23 VM's (ESXi 5.5) running off the spinning disk pool. the VM's are backup with vcenter and veeam backup. Is there a good way to backup the zvol extent though snapshots?

 

[Artion]

What I am wonder is if it possible\safe to share the whole pool. Every where I looked says if I go over 80% disk space I will inure a performance plenty and other bad things will happen.

It applies if you choose to use ZFS.

 

[rs225]

The warning about performance is for hard disk pools. It will not be significant on SSD.

 

[roundrobinknowledge]

So if I setup a raid 10 with the 4 SSD and then put a zvol extent that took all the space there should be nothing wrong?

 

[roundrobinknowledge]

Same goes if I instead used a raidz2 for the SSD

 

[rs225]

2 x 2-way mirror is usually preferred over raidz2 for iSCSI use.

Using all(100%) the space is not a good idea on ZFS no matter what you are doing. If you are going to use snapshots to backup, then you need to set aside some space equal to the rate of change in the pool over the entire period before snapshots are deleted. If you have 10GB of writes every day and snapshot once a day, and keep those for 30 days, you need 300GB of space just for that.

 

[roundrobinknowledge]

just to clear up a few things with the zvol extent. If you have a zvol that is running a database VM on it with constant changes can you expand the zvol and/or take a snapshots? From my understanding you can't expand it because iscsi would have write locks on it. If I understand snapshots it should be able to since it will write new data to delta files.

 

[rs225]

You can expand or shrink the zvol, but it might not be safe. You would have to test. I don't think any lock would prevent it.

You can snapshot, but your database may have rules on how to create a working snapshot while running. You should also test it.

 

[roundrobinknowledge]

From what I read on the forums it is a bad idea to expand a zvol in use. The produce I get out of it is to shutdown the connection to the iscsi extent and then stop the iscsi service on freenas then expand the zvol. after all that a person should be able to start service and reconnect the ESXi servers.

The SSD are 1 TB and assuming RAID10 so 2TB max, how much space can I give to a zvol for use on iscsi. I plan on it only to be used by VM's

 

[roundrobinknowledge]

I would prefer to some how give the SSD pool as an extent instead of a file or zvol