What needs to be flushed to disk will be flushed to disk. And ZFS never does in-place overwrites. So if you write every 5 seconds or 18 times the transaction groups every 90 seconds ...If @tverweij running virtualised instances is indeed using ZFS that specifically is a bad idea. Due to its copy on write nature you cannot thin provision virtual disks (well you can, but it doesn't make sense) because ZFS will eventually write every single disk block and so blow up the disk to its configured maximum size.For virtual disks it's much better to use UFS and manage snapshots and backups at the hypervisor host level.
Hi Franco,according to my understanding of ZFS it won't make much of a difference if you flush transaction groups every 5 or every 90 seconds. What needs to be flushed to disk will be flushed to disk. And ZFS never does in-place overwrites. So if you write every 5 seconds or 18 times the transaction groups every 90 seconds ...If @tverweij running virtualised instances is indeed using ZFS that specifically is a bad idea. Due to its copy on write nature you cannot thin provision virtual disks (well you can, but it doesn't make sense) because ZFS will eventually write every single disk block and so blow up the disk to its configured maximum size.For virtual disks it's much better to use UFS and manage snapshots and backups at the hypervisor host level.HTH,Patrick
