[xs-devel] iSCSI Logical Block Size for XenServer

[Vinícius Ferrão]

Hello guys,

I’m setting up a new Pool and was reading about some specific considerations about iSCSI fine tuning with XenServer.

For example, I’m not sure which Logical Block Size I should use with XenServer, the default is 512, but I can configure it up to 4096 (4k).

The problem is how XenServer works internally with the Logical Block Size over iSCSI.

Thanks in advance,
Viníci

[Tobias Kreidl]

Vinícius,
My understanding is that extended block sizes are not currently supported natively, so stick with 512 for now. See also: https://xenorg.uservoice.com/forums/172169-xen-development

-=Tobias

Post by Vinícius Ferrão
Hello guys,
I’m setting up a new Pool and was reading about some specific considerations about iSCSI fine tuning with XenServer.
For example, I’m not sure which Logical Block Size I should use with XenServer, the default is 512, but I can configure it up to 4096 (4k).
The problem is how XenServer works internally with the Logical Block Size over iSCSI.
Thanks in advance,
Vinícius.

[Vinícius Ferrão]

Hello Tobias,

Thanks for the quick reply. But just to be completely clear... I’m aware about the local disks being used with 512 sectors, but in this case was the iSCSI SR, more specifically on the iSCSI Extent. Even here the same limitations happens?

On the storage side the disks configured with 4k sectors.

Thanks in advance,
Vinícius.

Post by Tobias Kreidl
Vinícius,
My understanding is that extended block sizes are not currently supported natively, so stick with 512 for now. See also: https://xenorg.uservoice.com/forums/172169-xen-development
-=Tobias

Post by Vinícius Ferrão
Hello guys,
I’m setting up a new Pool and was reading about some specific considerations about iSCSI fine tuning with XenServer.
For example, I’m not sure which Logical Block Size I should use with XenServer, the default is 512, but I can configure it up to 4096 (4k).
The problem is how XenServer works internally with the Logical Block Size over iSCSI.
Thanks in advance,
Vinícius.

[Tobias Kreidl]

Vinícius,
The storage block size will affect the performance and to some degree
capacity, for example, Windows tends to optimize things at the 4k block
level. These are in turn aligned with physical blocks on the device
itself. Some logical devices will allow for much larger blocking factors
than that (e.g., 8k, 16k, 32k, 64k, 128k).

So as long as it is a logical block size and not a physical block size,
that should be up to you to define and functionality will ultimately be
dictated by what the file system will work best with.

Where are you seeing this configuration option? For your particular
storage device, does the manufacturer provide any recommendations?

-=Tobias

Post by Vinícius Ferrão
Hello Tobias,
Thanks for the quick reply. But just to be completely clear... I’m aware about the local disks being used with 512 sectors, but in this case was the iSCSI SR, more specifically on the iSCSI Extent. Even here the same limitations happens?
On the storage side the disks configured with 4k sectors.
Thanks in advance,
Vinícius.

Post by Tobias Kreidl
Vinícius,
My understanding is that extended block sizes are not currently supported natively, so stick with 512 for now. See also: https://xenorg.uservoice.com/forums/172169-xen-development
-=Tobias

Post by Vinícius Ferrão
Hello guys,
I’m setting up a new Pool and was reading about some specific considerations about iSCSI fine tuning with XenServer.
For example, I’m not sure which Logical Block Size I should use with XenServer, the default is 512, but I can configure it up to 4096 (4k).
The problem is how XenServer works internally with the Logical Block Size over iSCSI.
Thanks in advance,
Vinícius.