10:57 a.m.
Good day,
Some controllers do not allow to set a 4k block on a boot device.
With some installations of Ovirt in the configuration of ssd for boot OS and hdd (4k) for
data domain, engine is installed on ssd with a block size of 512e and then transferred to
hdd 4k. and if I wanted to leave the engine on ssd (in a separate partition which will
also have a size of 512e), I encountered an incompatibility error between block sizes 512
and 4k (example glusterfs or when the data domain was configured as posix compliant fs).
NFS domain passed.
As I understand it, the NFS uses 512e as well as the drivers of the guest machines, and a
VM created on a domain with a 4k block will still have 512e. As a result, we have a block
of size 512 in any case.
Does it make sense to use devices with a 4k block at the present time? Is there any
configuration to take advantage of 4K?
Thanks in advance.
Best regards.
11:31 a.m.
On Wed, Jul 7, 2021 at 5:58 PM <radchenko.anatoliy(a)gmail.com> wrote:
With some installations of Ovirt in the configuration of ssd for boot
OS and hdd (4k) for data domain, engine is installed on ssd with a block size of 512e and
then transferred to hdd 4k.
What do we mean by transferring engine to another disk?
Engine is installed either on a host, or in a vm. On a vm, it always
using sector
size of 512 bytes, since we don't support vms with sector size of 4k. If enigne
in installed on a host, there is no such thing as "transfer" to
another host. You
can reinstall engine on another host and restore engine database using a
backup. Sector size does not matter in this flow.
Sector size for data domain is relevant only for gluster storage or
local storage.
These are the only storage domain types that can use 4k storage.
and if I wanted to leave the engine on ssd (in a separate partition
which will also have a size of 512e), I encountered an incompatibility error between block
sizes 512 and 4k (example glusterfs or when the data domain was configured as posix
compliant fs). NFS domain passed.
As I understand it, the NFS uses 512e as well as the drivers of the guest machines,
Yes, NFS is always using a sector size of 512 bytes since we don't
have any way to
detect the underlying device sector size.
and a VM created on a domain with a 4k block will still have 512e. As
a result, we have a block of size 512 in any case.
Yes, vms always see sector size of 512 bytes. qemu knows the underlying storage
sector size and align I/O requests to the underlying storage sector size.
Does it make sense to use devices with a 4k block at the present
time? Is there any configuration to take advantage of 4K?
Yes, the most attractive use case is VDO, which is optimized for 4k sector size.
Another use case is having disks with 4k sector size which may be cheaper or
easier to get compared with disk supporting 512e.
For block storage oVirt does not support devices with 4k sector size yet.
Nir
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Nir Soffer -
radchenko.anatoliy＠gmail.com