ZIL problems

[Richard Henry]

So I am finishing up my install and am having an issue. I have ready through the new user power point and manual quite a lot and they have been quite helpful, but I can't find anything through searches on this.

I have two 128GB SSD drives that I plan on using for ZIL as the unit will be an ESXi datastore for file storage. I get the following error message when I go into the ZFS Volume Manager, select my two drives and choose Log (ZIL) for my layout: "You need a data disk group". I don't see any other options any where to add anything to it.

Any help or a point in the right direction on this would be greatly appreciated.

 

[dlavigne]

Which version of FreeNAS?

Post a screenshot of how you select the devices in ZFS Volume Manager.

 

[Richard Henry]

The version is 9.2.1.3

Keep in mind that I could be doing this completely wrong. The box is up and running rather well. I just wanted to see if adding the ZIL helped increase performance or not and cannot find much on the actual configuration for this. The manual only seems to glance over that it is there.

 

[HoneyBadger]

Hi Richard,

We can't access that image on DropBox (403) - can you rehost on Imgur or something?

Also can you post your system configuration? I looked at your post history but all I could find was discussion on a 45-drive setup that was going to be used for media storage, not an ESXi datastore. Specifically interested in the amount of RAM and the type of SSDs you're using, as SSDs for SLOG should have power-fail prevention as well as a massive amount of underprovisioning to help with the wear-leveling.

 

[Richard Henry]

Sorry about that. I don't post images on forums to often. Mostly just text, lol. Here you go.

I do have the 45 drive setup and while it is being used for a lot of image storing, we felt it would work better over iSCSI as a Datastore than through NFS.
It is a Core i3 CPU with 32GB of RAM. The SSD's are from SANDISK, but I do not know the model as they came in the box when we purchased it. The unit is hooked up to three different UPS's that are each running at 20% load, so I am not sure worried about failure on that end.
I did read about under-provisioning it, but could not find much on how to do it properly when I was looking around.

 

[HoneyBadger]

You're trying to create a new volume there; you need to select an existing volume to extend instead of making a new one. Clear the "Volume Name" field and select your existing volume from the drop-down "Volume to extend" list - then add the SSDs as log devices.

If you're switching from an NFS datastore to iSCSI, bear in mind that ESXi doesn't send everything as a sync write to iSCSI. Unless you set sync=always on the dataset, you'll barely ever use those SSDs.

Underprovisioning has to be done from the command line by creating a single smaller (8G is usually fine) partition on the disks, and then using the zpool add command. In the example below, ada4 and ada5 are the SSDs, and the zpool is named "zpool1"

Code:

gpart create -s GPT ada4
gpart create -s GPT ada5
gpart add -t freebsd -a 4k -s 8G ada4
gpart add -t freebsd -a 4k -s 8G ada5
zpool add zpool1 log mirror ada4p1 ada5p1

 

[Richard Henry]

Thanks so much HoneyBadger. That makes a ton of sense now.

 

[joeschmuck]

I'm just curious if adding a ZIL provides you any real world benefits. I would have thought adding more RAM would give you better results, however I don't know your system setup/usage and I know SSDs can be cheaper than replacing RAM.

 

[HoneyBadger]

Assuming he enables sync writes for iSCSI (which ensures data integrity) then yes, SLOG will absolutely give massive tangible real-world benefits here.

 

[Richard Henry]

So the first four commands completed successfully. 3 and 4 created ada0s1 and ada1s1
I then put in: zpool add zpool1 log mirror ada0s1 ada1s1
I get the error: cannot open 'zpool1': no such pool

I also cannot for the life of me find where to set the sync=always. I am typically fairly good at researching and finding things on my own, however it does not seem to be the case between the manual, forums, and internet with FreeNAS. So I really appreciate all of the help.

 

[Richard Henry]

Ok, on the last part...am I correct that I just run the following command: zfs set sync=always

 

[Richard Henry]

Now for the first part: I am not going to edit it so that I be reminded of how dumb one can be sometimes
I have always had a problem with syntax until I see a full blown example of how it works. After reading through some other forum posts, I now understand how it works. I was also able to follow the usage guide to figure out the sync part, so I am all good now and will test out how this is working.

 

[HoneyBadger]

So the first four commands completed successfully. 3 and 4 created ada0s1 and ada1s1
I then put in: zpool add zpool1 log mirror ada0s1 ada1s1
I get the error: cannot open 'zpool1': no such pool

I also cannot for the life of me find where to set the sync=always. I am typically fairly good at researching and finding things on my own, however it does not seem to be the case between the manual, forums, and internet with FreeNAS. So I really appreciate all of the help.

You'll need to substitute the name of your zpool; the example I gave was for someone with it named "zpool1" - so if your pool is named "RichardsPool" you would need

Code:

zpool add RichardsPool log mirror ada0s1 ada1s1

And similarly you need to specify the pool when using the zfs command, so sync would be

Code:

zfs set sync=always RichardsPool

 

[joeschmuck]

Assuming he enables sync writes for iSCSI (which ensures data integrity) then yes, SLOG will absolutely give massive tangible real-world benefits here.

Thanks, good to know.