ZFS Sync Disabled?

[killmasta93]

Hi,
I was wondering how dangerous would it be running ZFS with sync disabled when it was previous on standard? As with standard im getting 80 fsync which i can work with vm using linux but on windows its impossible. But putting disabled i get 2300 fsync. Currently using 3X1TB 7200RPM with RAIDZ-1. My other question i also disabled zfs compression which i read it helps with performance but is necessary to have it on? And my last question when creating a VM, how risky is also running write back rather then default?
The idea is to have atleast 1k of fysnc min for just 2VMs one is pfSense which works great, but on windows 2012r2 alots of lag. I know that adding SSD which helps but currently want to test it out without the ssd.

Which combination should i use for windows server 2012r2?
ZFS=DISABLED----on disk vm default or none or writethrough
ZFS=Standard----on disk vm default or none or writethrough


Thank you

 

[Nemesiz]

Protect your server with UPS and it totally safe to use sync=disabled

https://forum.proxmox.com/threads/p...-ssd-drives-sync-parameter.31130/#post-155543
https://forum.proxmox.com/threads/p...-ssd-drives-sync-parameter.31130/#post-155543
As for VM disk I use default. I don`t think others methods give you better advantage or more safety.

 

[killmasta93]

Thanks for the quick reply, i was reading it shows that its somewhat dangerous? Ofcourse it has UPS but lets say the UPS gets somehow damaged and the server just a shutdown forcefully what are the outcomes?
When they say info lost meaning the info that was stored previous or during the shutdown?
and for the VM disk so just keep it simple? default? what is better writes or read for windows server?

Thank you

 

[Nemesiz]

ZFS is COW (copy-on-write) file system. In the past few years I had no data corruption with sync=disabled and in that period I can count minimum 10 electricity power lost or software fatal error.

What you can loose is 5 last seconds of new data. In heavy write it can be longer but no data corruption.

 

[killmasta93]

Thanks for the quick reply, For now i will go using sync=disabled just because its a test server, but i was wondering if adding an SSD and install the OS proxmox and partition the disk to logs and cache would that keep atleast the fsync to 2000? using somewhat this guide?
https://tekwiki.beylix.co.uk/index.php/Proxmox_+_ZFS_with_SSD_caching:_Setup_Guide

Thank you

 

[Nemesiz]

ZFS writes to ZIL from begging and repeat it every time. ZIL is not like COW. SSD can wear out very fast. Keep it in mind then you buy SSD for ZFS log.

 

[guletz]

My other question i also disabled zfs compression which i read it helps with performance but is necessary to have it on?

On most of the cases, zfs compression will improve the performance. Think like this:
- if the blocks who are need to be write to the disk, are un-compressible the blocks are write as they are
- but if let say you have some compressible blocks, is possible to need to write less (compressed)blocks to disks = better IO/disk bandwith
- and the extreme case, if you need a file with many holes(with 0 data), in this case the compression is very usefull also

 

[killmasta93]

On most of the cases, zfs compression will improve the performance. Think like this:
- if the blocks who are need to be write to the disk, are un-compressible the blocks are write as they are
- but if let say you have some compressible blocks, is possible to need to write less (compressed)blocks to disks = better IO/disk bandwith
- and the extreme case, if you need a file with many holes(with 0 data), in this case the compression is very usefull also

Thanks for the reply, very interesting information did not know, i just enabled it again. I was wondering if running 2X 1tb ZFS RAID 1 for the proxmox OS and the the 3X1tb for the VMs would that help on the performance and leaving sync=standard? as im guessing the logs and cache are done on the OS ?

 

[guletz]

Thanks for the reply, very interesting information did not know, i just enabled it again. I was wondering if running 2X 1tb ZFS RAID 1 for the proxmox OS and the the 3X1tb for the VMs would that help on the performance and leaving sync=standard? as im guessing the logs and cache are done on the OS ?

No, this will not help you for better performance. Also you need to know that without any info about WHAT load dou you have any responses are usefull for your case.
If I ask you what car is OK for you, a disel or a gas engine? What will be your best response ?

 

[killmasta93]

Thanks for the reply, and sorry to neglect the info well, the load is minimal as this is a test enviroment, 2 Vms one running pfSense 1.5k of ram and another VM windows server machine with 4k of ram, hardware is running 8k ram using around 70% since disabling sync=disabled the windows machine is flying great. as future going to put SQL database which worries about the data lose unless i figure out how to turn off proxmox with the APC-UPS

 

[guletz]

Thanks for the reply, and sorry to neglect the info well, the load is minimal as this is a test enviroment, 2 Vms one running pfSense 1.5k of ram and another VM windows server machine with 4k of ram, hardware is running 8k ram using around 70% since disabling sync=disabled the windows machine is flying great. as future going to put SQL database which worries about the data lose unless i figure out how to turn off proxmox with the APC-UPS

zfs and SQL is a very different story. For APC is simple, search with apt after apc/ups.