openzfs/zfs

Allow configuration of zvol logical blocksize

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#4,203 opened on Jan 11, 2016

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Component: ZVOLType: Featuregood first issue

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Description

The logical blocksize of a zvol seems to always be 512 byte, despite the fact that volblocksize is set to 4 KB:

# zfs get volblocksize data/iscsi 
NAME        PROPERTY      VALUE     SOURCE
data/vol1   volblocksize  4K        -

# lsblk -o name,min-io,opt-io,phy-sec,log-sec,rq-size
NAME    MIN-IO OPT-IO PHY-SEC LOG-SEC RQ-SIZE
zd0       4096   4096    4096     512     128

Is there any way to set logical blocksize = physical blocksize?

Contributor guide

Research direction
Inspect the zvol driver code (e.g., module/zfs/zvol.c) to see how logical block size is set. Look for the function that creates the block device and determine where the logical block size (e.g., queue logical block size) is assigned. Then design a solution to make it configurable via a module parameter or zfs property, ensuring it does not exceed volblocksize. Implement and test.
Tech stack
c
Domain
backend
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
CZFS architectureLinux kernel device drivers
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20