Don,

Sorry, I wasn’t clear in my previous e-mail. My comment about small disks actually is about how much disk space you have currently in use, not the virtual disk size.

For example, I have a 200GB virtual disk VM with only 4,6 GB in use. It takes about 40 sec to transfer the disk to an NFS share in my lab reaching 128MiB/sec on a 1Gbps network connection.

Marcos

From: Don Dupuis <dondster@gmail.com>
Sent: Monday, November 11, 2024 11:32 AM
To: Marcos Sungaila <marcos.sungaila@oracle.com>
Cc: users <users@ovirt.org>
Subject: Re: [External] : [ovirt-users] oVirt slow backups from ISCSI storage domain to nfs target

Marcos,

These are not small files, the files I am talking about are about 400GB or bigger. If I do the same thing on another DE6000 with SAS disks, I don't see this issue. Thin provisioned disks are ok on both storage systems, But the 6600F has NVME interfaced SSDs and runs this slow on preallocated disks. For the short term we are just going to go back to thin provisioned as we can't get the backups to finish in the allocated time windows.

Don

On Mon, Nov 11, 2024 at 5:23 AM Marcos Sungaila <marcos.sungaila@oracle.com> wrote:

Hi Don,

When transferring small files to an NFS share, many times, they can fit the in-memory cache, leading to high transfer rates. For bigger files, the remote NFS storage will need to commit data to the disk once the cache is filled.

In general, it is common to see the initial data transfer at high numbers, slowing down as the transfer continues. This behavior is not only with NFS shares; you may face the same behavior using scp.

Anyway, it is recommended that a transfer test be run using other methods to confirm this is the cause.

Marcos

From: Don Dupuis <dondster@gmail.com>
Sent: Friday, November 8, 2024 5:06 PM
To: users <users@ovirt.org>
Subject: [External] : [ovirt-users] oVirt slow backups from ISCSI storage domain to nfs target

Hi

I am using oVirt 4.4.10.7 with vms on iscsi Lenovo DE-6600F(nvme interfaced ssds). Backing up thin vms performance is fine, but with preallocated disks, backups to nfs storage with 200Gb interface is only transferring qcow2 image to nfs at 140MiB per sec. Why is qemu-nbd so slow with preallocated images? Does anyone have any issues related to this? Any help would be appreciated. I have made iscsid.conf changes, linux kernel boot changes, and still the same performance.

Thanks

Don