ESXi iSCSI and the "50% Rule"

[zimmy6996]

Hey all! Looking to clarify something. This message is really for @jgreco but anyone with knowledge of the topic might be able to help ....

Here is the background of my setup ...

STORAGE POOL
8 x 3TB Mirrors - Total 24TB of Storage

Defined a 12TB ZVOL (which is 50% of total space)
* Noticed it warns not to use more than 80% of available space for ZVOL.

Created iSCSI Extent for VMWARE using a ZVOL device.

Target Golbal Configuration
Pool Available Space Threshold - 50%

Extent Confgiuration (were i configure Extent type to device, etc ...)
Available Space Threshold - 50%

Basically, what I'm trying to figure out with respect o best practice ... I know as a rule of thumb you should stay under 50% usage ... What I'm trying to understand is ... Is this a "storage pool" suggestion, or a "ZVOL" suggestion? Basically, what I'm getting at here ... I've only allocated 50% of the pool for a ZVOL, and then i've got these alerts set for 50%. Which gives me the sense that I really only can use 6TB of my 24TB of storage. Seems that I'm looking at this wrong ...

Basically, should I allocate that ZVOL to 80% or so of my usable pool storage. Maybe raise it up to 19.2TB vs the 12TB it is at now. Expand my ZVOL to 19.2TB, and then keep the the iSCSI usage to under 10TB? Or am I really to believe that your best practice ends up being only 25% of usable storage? Just trying to make sure I figure this out before I get "too far down the rabbit hole".

Just to be clear, the FREENAS is only an ISCSI mount for ESXi. There are no additional datasets on there for CIFS/NFS mounts ...

Your valued advice would be greatly appreciated!

 

[dlavigne]

I know as a rule of thumb you should stay under 50% usage ... What I'm trying to understand is ... Is this a "storage pool" suggestion, or a "ZVOL" suggestion?

From http://doc.freenas.org/9.10/sharing.html#extents:

For performance reasons and to avoid excessive fragmentation, it is recommended to keep the used space of the pool below 50% when using iSCSI.

 

[zimmy6996]

From http://doc.freenas.org/9.10/sharing.html#extents:

For performance reasons and to avoid excessive fragmentation, it is recommended to keep the used space of the pool below 50% when using iSCSI.

I understand, so the question is ...

Do I define a ZVOL in my pool that is 50% of the size of the pool, and then feel free use use 80-90% of the iSCSI extent?

Do I define a ZVOL in my pool that is 80-90% of the size of the pool, define and EXTENT, using ZVOL, and then then ensure only 50% is used?

Basically, what I'm trying to figure out is am I really forced to use only 25% of the available space, (ZVOL 50% of POOL SIZE, AND THEN ENSURE ONLY 50% USAGE OF THE ZVOL/ENTENT) or can I use 50% of the pool size be definding a ZVOL that is about 80-90% of the POOL size, thin-provisioned, and then insure that the ZVOL/POOL only hits 50% usage?

 

[Ericloewe]

No, it's 50% of the pool. The filesystem operating on the block device will naturally not react too well to a very full drive, so just size the zvol a bit higher than 50%.

 

[darkwarrior]

Hi there,
on that particular topic you need to think "less than 50% of Pool usage", if performance is a key factor.
You could create a sparse Zvol as big as your pool (Attention !!! Not recommended, GUI will actually insult you), this would not be a problem as long as you keep the pool usage under 50% at all times.

I'm running iSCSI to store files and the performance got quite unpleasant when adding files, since I moved past the 60% "Pool space used"- mark ...

Edit: Eric beat me to it :P