Will Dormann
Explorer
- Joined
- Feb 10, 2015
- Messages
- 61
Hi folks,
I've got FreeNAS 9.3 on a system with 10GbE and 256GB of RAM. I'm setting up iscsi for use with esxi, and I'm using the zvol route to get the VAAI accelration that FreeNAS now supports it. I've noticed that the "sync=always" zfs setting has a huge hit on performance, regardless of the speed of the underlying disks.
In my case, I've got the zfs equivalent of a 4-drive RAID10 of SSDs. If a VM lives in the SSD-based datastore in vSphere, a simple "dd" test (dd if=/dev/zero of=zero bs=1M) shows that it can write at just over 60MB/sec if sync=always is set for the zpool (or zvol) in question. If I change sync=standard, the throughput goes to close to 650MB/sec.
Is this expected? If sync=always has such a large performance penalty, what are the cases where it would make sense to use?
Thanks.
I've got FreeNAS 9.3 on a system with 10GbE and 256GB of RAM. I'm setting up iscsi for use with esxi, and I'm using the zvol route to get the VAAI accelration that FreeNAS now supports it. I've noticed that the "sync=always" zfs setting has a huge hit on performance, regardless of the speed of the underlying disks.
In my case, I've got the zfs equivalent of a 4-drive RAID10 of SSDs. If a VM lives in the SSD-based datastore in vSphere, a simple "dd" test (dd if=/dev/zero of=zero bs=1M) shows that it can write at just over 60MB/sec if sync=always is set for the zpool (or zvol) in question. If I change sync=standard, the throughput goes to close to 650MB/sec.
Is this expected? If sync=always has such a large performance penalty, what are the cases where it would make sense to use?
Thanks.
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