Removing ZIL from zpoolq

[Dave Genton]

Another way(and vmware recommends) is to make sure traffic is isolated. One nic for vm's one for afp.

I'm a Data Center Engineer / Consultant professionally and have been doing it over 20 years. Past 5 dedicated to Data Center virtualization, storage, and converging fabrics. I'm VMware Certified among many others so my home and lab networks are designed like they are in the real world. Done with best practices and proven designs. Both my home and lab networks have dedicated NIC's and uplinks for iSCSI, network just for SAN/Storage traffic and replication, NIC's for user shares, NIC's for mgmt, etc. More often than not I also utilize the Cisco Nexus 1000v virtual switch in ESXi for vm switching when I need total control like for quality of service and marking frames accordingly or just a entry point in the virtualized "gray" part of the network to mirror packets for capture.

 

[Dave Genton]

Have you seen a difference between NFS and iSCSI in regards to the sync performance?

I selected iSCSI when I setup my target. I was under the impression at the time (maybe a false one) that NFS wanted to do EVERYTHING as a sync coming out of ESX to it's target. With iSCSI, I thought I read that it was more of a choice that ESX made based on the who/what. I don't have any articles to back that up, but I thought I read one of the ninjas on here explaining it.

My pool is set for sync=standard. I would rather do sync=all, but I don't have an appropriate hardware config for it yet (currently using a RAID controller cache with battery), so I have to choose between bad performance or bad data integrity. This is a test system as you mentioned, so I'm willing to make the poorer of the two choices.

I keep switching between standard and all just to compare for fun, I'm curious what yours looks like.

Did I see a difference when I set it to disabled ?? YES, BIGTIME. It was night and day when it comes to ESXi writing to FreeNAS with NFS and iSCSI. iSCSI already pretty good but NFS sucks, always. With it off it does indeed make a difference so I know what the issue is. Mine is set to standard.

I'm back in my lab and despite what I just said above, I still want to find a way to design my system so I can archive or push copies of all my lab virtual machines to FreeNAS for backups but without it taking 18 hours to do it. If I can pull it back in a few hours then I can push it in a few hours but just have to over come some obstacles.

 

[Dave Genton]

Can you just run a pure iostat while you are running your tests? That should show us if the zil is being written to. I would ssh in while testing. Although the ssh traffic may interfere slight with workload. Best if done on a second nic.

#iostat -v 1

After awhile hold "control" and type "c"

Sorry did a search while logged in and see the command is "zpool" then what you posted. have it running now, thanks.

 

[Dave Genton]

Can you just run a pure iostat while you are running your tests? That should show us if the zil is being written to. I would ssh in while testing. Although the ssh traffic may interfere slight with workload. Best if done on a second nic.

#iostat -v 1

After awhile hold "control" and type "c"

I have it running while I am having vmware transfer large amounts of data onto an NFS Share it owns on the FreeNAS box and I am not seeing anything hit the log SSD I have installed. I see the bandwidth go over 100M and writes are equally striped across all drives in the zpool but zero traffic on the LOG device. Once a transfer is completed and all the write traffic is done I then see a little flury of activity hitting the log for a second but just kb's literally for maybe a second.

Well I was going to ask why I didn't see anything but wanted to start iSCSI and test. I reset the iostat and noticed something. When I have it running as you requested with an interval it doesn't show any activity for the log. When I remove the interval and just request an output at that given time it always shows log activity. Is this a bug ?? Any other command like the one you showed me where I CAN see log while data is transferring vs just a snapshot in time ??