ZIL through ESXi, or direct to VM?

[JamesP]

I'm running an ESXi server hosting a NAS4FREE VM. I have an M1015 SAS card that I pass through to the VM using VT-d and I have 6 disks connected to the card in a raid-z2 configuration.

I'm about to add a 100GB ZIL drive (Intel S3700) and I see two ways to do this. I could put the drive on the M1015 but then only the NAS4FREE VM would have direct access to the drive. Considering that I only need 8-16GB for a ZIL drive (max RAM on my system is 32GB), it seems like a waste of 90 GB of space.

The other option is to create an ESXi datastore on the drive, create a 16GB virtual disk and forward this disk to the NAS4FREE VM. Presumably, there would be some sort of a performance hit on the ZIL, but at least I'd be able to use the remaining 80+GB with other VM's.

Am I missing something that might sway me towards putting the ZIL on the M1015 card?

Thanks,
James

 

[brutalizer]

Test both scenarios and report here? You can add and detach a ZIL without problems.

 

[JamesP]

Test both scenarios and report here? You can add and detach a ZIL without problems.

Sure, will do. I was just wondering of someone knew of a dealbreaker with using the SSD through ESXi as a ZIL drive so I wouldn't have to bother trying that option. Such as "once you go through esxi you lose so much performance that it's like not even having a ZIL".

I'm hoping I can get to try this during the weekend.

BR,
James

 

[JamesP]

Test both scenarios and report here? You can add and detach a ZIL without problems.

I did manage to test both configs during the weekend and here are some numbers I measured. I used Iometer to measure performance (my first time using iometer...) and all measurements are for write operations. The test file created by dynamo on the client was about 2GB in size and the client was configured for 1GB of RAM. IIRC, dd writes maxed out at 100MB/sec.

ESXi hosting an Ubuntu 12.04 VM where the datastore is exported via NFS from a NAS4FREE server hosted by the same ESXi instance. No ZIL drive.

Request-Size Operations/sec Throughput(MB/sec)
  4k 67 0.3
  8k 74 0.6
 16k 72 1.1
 32k 70 2.0
 64k 40 2.3
128k 20 2.4

Here I added the S3700 ZIL drive directly connected to the M1015:

Request-Size Operations/sec Throughput(MB/sec)
  4k 2.6k 10
  8k 1.7k 12
 16k 1.8k 29
 32k 1.2k 38
 64k 1.1k 70
128k 0.7k 86

MUCH faster!

Here I connected the S3700 directly to the motherboard and configured it as an ESXi datastore. I created a 16GB virtual drive on that datastore and passed it to the VM and added it as a ZIL drive:

Request-Size Operations/sec Throughput(MB/sec)
  4k 2.9k 11
  8k 1.9k 14
 16k 2.2k 30
 32k 1.1k 34
 64k 1.2k 68
128k 0.7k 91

This last setup is the configuration I'm going to go with since it gives me flexibility to use the extra space on the drive for other purposes.

JP