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[Bug 1884831] Re: qemu-nbd fails to discard bigger chunks
From: |
Eric Blake |
Subject: |
[Bug 1884831] Re: qemu-nbd fails to discard bigger chunks |
Date: |
Fri, 07 May 2021 12:30:28 -0000 |
Commit 890cbccb0 included in upstream release 5.1.0.
** Changed in: qemu
Status: Incomplete => Fix Released
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https://bugs.launchpad.net/bugs/1884831
Title:
qemu-nbd fails to discard bigger chunks
Status in QEMU:
Fix Released
Bug description:
This report is moved from systemd to here:
https://github.com/systemd/systemd/issues/16242
A qemu-nbd device reports that it can discard a lot of bytes:
cat /sys/block/nbd0/queue/discard_max_bytes
2199023255040
And indeed, discard works with small images:
$ qemu-img create -f qcow2 /tmp/image.img 2M
$ sudo qemu-nbd --connect=/dev/nbd0 /tmp/image.img
$ sudo blkdiscard /dev/nbd0
but not for bigger ones (still smaller than discard_max_bytes):
$ qemu-img create -f qcow2 /tmp/image.img 5G
$ sudo qemu-nbd --connect=/dev/nbd0 /tmp/image.img
$ sudo blkdiscard /dev/nbd0
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