On Sun, 5 Mar 2017 15:09:39 -0500, James Blachly wrote:
ZFS on Linux has had a feature "Disable LBA weighting on SSD" since August 2015:
http://open-zfs.org/wiki/Features#Disable_LBA_Weighting_on_files_and_SSDs
https://github.com/zfsonlinux/zfs/commit/fb40095f5f0853946f8150481ca22602d1334dfe
Because we have the driver property "device-solid-state" we can port this over.
In addition, we should add detection for virtio vioblk device, which should also not use
LBA weighting.
On linux, block devices have a "non-rotational" property, so this is a one
liner in vdev_disk.c:
v->vdev_nonrot = blk_queue_nonrot(bdev_get_queue(vd->vd_bdev));
We do not, so the checks are a little bit more cumbersome but doable (check
device-solid-state != 0 and inquiry-vendor-id==Virtio separately)
QUESTIONS
1. Linux has a non rotational property for block devices. Should we? By moving
this out of ZFS it could be used in other places. Besides SSD, this property
would apply to zvols, Virtio disks, and potentially in the future, network
block devices (e.g. ceph)
2. Is there a better or more preferred way to check for a Virtio vioblk device
besides checking inquiry-vendor-id ?
3. Since this is a straight port of all but the code in vdev_disk.c, I did not
add copyright messages. This will cause git pbchk to gripe. How is this
typically handled?
4. OpenZFS developers: your repo is out of sync with illumos-gate; I don’t know
how to create a PR on github that does not also include other commits not yet
merged into your fork. Pointers appreciated.
Make changes against cloned openzfs repository, but push them as a
branch into your illumos-gate fork, eg:
git clone [email protected]:openzfs/openzfs.git
git remote add illumos <your-fork>
<make changes>
git push illumos master:<new-branch>
and then create PR from that branch.
---
Issue: https://www.illumos.org/issues/7938
Webrev: http://cr.illumos.org/~webrev/jblachly/zfs_lba_weighting/
Git commit:
https://github.com/jblachly/illumos-gate/commit/863ed00ba3278bfec58a0edb504ad484fac0c10b
WRT the change itself - please correct me if I'm wrong, but looks like
all possible rotational disk are driven by sd(7D), so if the parent
isn't sd, it's not rotational - blkdev, which is yours "Virtio", any others?
For the sd itself, we could enhance the sd_check_solid_state() to set
non-rotational device property is "Block Device Characteristics" VPD
reports RPM == 0 (for SSDs RPM == 1) - e.g., for pvscsi disks I'm
getting RPM == 0, same would go for iscsi, etc.
-------------------------------------------
openzfs-developer
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