Sad Clouds <cryintothebluesky%gmail.com@localhost> writes: > On Wed, 17 Feb 2021 13:15:39 -0500 > Greg Troxel <gdt%lexort.com@localhost> wrote: > >> >> Suppose I create a 16G zvol on a pool that is a disklabel partition on >> an SSD. I would expect read/write performance that is near the >> native SSD read/write speed. > > Why would you expect that? In other words, you're expecting that a > complex file system like ZFS would have near zero overheads, which is > not possible. When you take into considerations things like checksums, > compression, encryption, etc, then the overheads could be quite > significant. I have not enabled compression or encryption, and I forgot about checksums. However, the use case for zvol is having zfs being a logical volume manager, and it would seem reasonably feasible to get high efficiencies via allocation of large numbers of blocks at once. So 10-20% slower wouldn't surprise me. Have you used zvols? What was your experience?
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