VMware 6.7 Datastore block size

[KAvarajo]

Hi All,

I wish to use the latest version of FreeNAS to host my VMware datastores (iscsi). I downloaded and installed version 11.2 U4.1 into:
Dell: R620
Mem: 48 G Ram
CPU: 16 Cores

My question, if I want to create a datastore what the block size I should select when creating the Zvol? (There is no 1024 from the drop-down list?) or just keep it 64K? whats the recommendation here?

To set 1M block size, I set the record size of the pool to 1M and when I created the Zvol I set the block size to inherit? thought?

Thanks in advance
HY.

 

[dlavigne]

Did you find a definitive answer for this?

 

[jgreco]

Did you find a definitive answer for this?

It does seem a little strange that common usage models like this don't have some specific guidance in the manual, at least last I checked.

 

[HoneyBadger]

My question, if I want to create a datastore what the block size I should select when creating the Zvol? (There is no 1024 from the drop-down list?) or just keep it 64K? whats the recommendation here?

The proper block size to choose for the ZVOL depends on what kind of data you plan to store. For general purpose VMs, either 16K or 32K is usually the best balance between latency and throughput. For other datasets that have a specific recommended allocation size follow the vendor's guidelines, eg: SQL log is 64K, most OLTP DBs are 8K - however, smaller recordsize means potentially less max throughput and less efficient compression.

To set 1M block size, I set the record size of the pool to 1M and when I created the Zvol I set the block size to inherit? thought?

ZVOLs use a separate parameter which is volblocksize - the setting for recordsize on a parent doesn't impact them. A recordsize that large I would only recommend for a VMDK that will hold large media files, and I would ask why not just share the files directly from FreeNAS via a NAS protocol (SMB/NFS) instead.

It does seem a little strange that common usage models like this don't have some specific guidance in the manual, at least last I checked.

The default volblocksize of 16K is a sane default that generally works well in most cases, but getting it "right" does involve a little more; maybe I'll see about putting in a documentation update or making a resource thread here.