Daz’s bits and bobs

Since im using ZFS as storage via NFS for my some of my vmware environments i need to ensure that latency on my disk is reduced where ever possible.

There is alot of talk about ZFS compression being “faster” than a non-compressed pool due to less physical data being pulled off the drives. This of course depends on the system powering ZFS, but i wanted to run some tests specifically on latency. Throughput is fine in some situations, but latency is a killer when it comes to lots of small reads and writes (in the case of hosting virtual machines)

I recently completed some basic tests focusing on the differences in latency when ZFS compression (lzjb) is enabled or disabled. IOMeter was my tool of choice and i hit my ZFS box via a mapped drive.

I’m not concerned with the actual figures, but the difference between the figures

I have run the test multiple times (to eliminate caching as a factor) and can validate that compression (on my system anyhow) increases latency

Basic Results from a “All in one” test suite… (similar results across all my tests)

ZFS uncompressed:

IOps : 2376.68
Read MBps : 15.14
Write MBps : 15.36
Average Response Time : 0.42
Average Read Response Time : 0.42
Average Write Response Time : 0.43
Average Transaction Time : 0.42

ZFS compressed: (lzjb)

IOps : 1901.82
Read MBps : 12.09
Write MBps : 12.28
Average Response Time : 0.53
Average Read Response Time : 0.44
Average Write Response Time : 0.61
Average Transaction Time : 0.53

As you can see from the results, the AWRT especially is much higher due to compression. I wouldn’t recommend using zfs compression where latency is a large factor (virtual machines)

Note: Under all the tests performed the CPU (dual core) on the zfs box was never 100% – eliminating that as a bottleneck.

To share your zfs pool via NFS (that works with Citrix Xen / ESX) to a host called “esxhost”;

zfs set sharenfs=rw,nosuid,root=esxhost tank/nfs

Note : You MUST have a resolvable name from the opensolaris box. i.e. you should be able to ping it. I have tried with ip’s only and it will fail. I have edited the /etc/hosts file to include the following line for my config;

# Copyright 2007 Sun Microsystems, Inc. All rights reserved.
# Use is subject to license terms.
#
# ident “%Z%%M% %I% %E% SMI”
#
# Internet host table
#
192.168.9.120 esxhost

This also requires that you are using both DNS and Files in your /etc/nsswitch.conf file. You should have a line like so;

# You must also set up the /etc/resolv.conf file for DNS name
# server lookup. See resolv.conf(4). For lookup via mdns
# svc:/network/dns/multicast:default must also be enabled. See mdnsd(1M)
hosts: files dns mdns

# Note that IPv4 addresses are searched for in all of the ipnodes databases
# before searching the hosts databases.
ipnodes: files dns mdns

i’ve also run this before hand; (to allow full access)

chmod -R 777 /tank/nfs

Update : check this guide http://blog.laspina.ca/ubiquitous/running-zfs-over-nfs-as-a-vmware-store

This is something i do in the lab so all of my vm’s are able to access iso’s etc (very handy for quick builds). Quite handy doing it through windows since its easiey enough to setup a windows network share to the same location and update various files via that.

This site has some good clear instructions : http://vmetc.com/2008/02/19/create-a-nfs-share-for-vm-iso-files-with-windows-2003-server-r2/

1. On the Windows 2003 Server make sure “Microsoft Services for NFS” in installed. If not you need to add it under Add/Remove Programs, Windows
   Components, Other Network File and Print Services
2. Next go to folder you want to share and right-click on it and select Properties
3. Click on the NFS Sharing tab and select “Share this Folder”
4. Enter a Share Name, check “Anonymous Access” and make sure the UID and GID are both -2
5. In VirtualCenter, select your ESX server and click the “Configuration” tab and then select “Storage”
6. Click on “Add Storage” and select “Network File System” as the storage type
7. Enter the Windows Server name, the folder (share) name and a descriptive Datastore Name
8. Done. Now you can map CD iso’s to your various vm’s.