NetApp thin provisioning for VMware

Thin provisioning is a popular buzzword, especially when it comes to NetApp. However, it can really save you time and headache in a number of situations. We use thin provisioning while presenting NFS volumes from NetApp to VI3 ESX hosts. Well, NetApp already let you change size of its FlexVol volumes on the fly. But you need to do it manually. Thin provisioning helps you to configure volumes so that in case of space shortage on a volume it will automatically expand without manual intervention. Of course you need to look after your volumes, otherwise they can fill all your storage space. But it will save you enough time to resolve data growth problem. Without thin provisioning in such situation your applications can easily crash.

NetApp doesn’t support iSCSI thin provisioning for VMware, so NFS is the only option. Don’t be afraid of performance issues. Without a doubt it’s slower than FC, but NetApp is famous for its NFS performance and it’s very well suited for mid-level workloads.

To be more specific, using thin provisioning you can create say 300GB virtual hard drive for particular VM and it will initially use no space. Then it will grow as long as you fill it. It can save you tremendous amount of storage space. Because you never exactly know ahead how much space you need. But be aware, if you will try to migrate thin provisioned virtual hard drive using storage migration plugin for VMware Virtual Center then it will fill all space. It means 300GB will use all 300GB even if it’s half-full.

The best article which will help you to integrate NetApp with VMware VI3 is NetApp TR-3428: NetApp and VMware Virtual Infrastructure 3 Storage Best Practices. What I will write here are basically excerpts from this article.

NetApp Configuration

Lets start from the NetApp configuration. First thing to do is to disable snapshots as usual. Generally it’s not a good idea to make snapshots of VMware virtual hard drives on the fly. They won’t be consistent. I will touch this topic in my later posts.

> snap sched <vol-name> 0 0 0
> snap reserve <vol-name> 0

Next step is to disable access time update on the volume, which is safe because VMware doesn’t rely on accurate access time for its files. It will increase performance, since Filer won’t need to update access time for files each time they are read or written.

> vol options <vol-name> no_atime_update on

Then configure the thin provisioning feature itself by switching volume auto size policy to on. It has two keys -m and -i. By -m you set maximum volume size and by -i you configure increment size.

> vol autosize <vol-name> [-m <size>[k|m|g|t]] [-i <size>[k|m|g|t]] on

NetApp recommends to disable Fractional Reserve for thin provisioned volumes, it’s just not needed anymore. Fractional Reserve guarantees successful writes to volumes in case you use snapshots. According to how snapshots work if you completely overwrite snapshot data you will use double amount of storage space. And it’s where Fractional Reserve comes into place. It reserves 100% of additional space for such cases. It means you will never run into situation when you are out of space due to active snapshots. But since we enabled auto size, our volume will resize on demand and Fractional Reserve becomes redundant. Supposedly auto size was implemented little bit later than Fractional Reserve and we have both of them in NetApp.

> vol options <vol-name> fractional_reserve 0

In case you use snapshots as a tool for instant VMware block level backups you can change auto delete policy. I said earlier that you should disable snapshot schedule, however you can manually (using scripts) create consistent snapshots. If you want to do that then you can additionally instruct NetApp to delete oldest snapshots when you are out of space on Filer and can’t auto grow volume.

> snap autodelete <vol-name> commitment try trigger volume target_free_space 5 delete_order oldest_first
> vol options <vol-name> try_first volume_grow

Now we need to create NFS export on NetApp Filer. It’s where FilerView interface comes handy. In short, you should give your ESX hosts read-write access, root access and configure Unix security style.

VMware Configuration

VMware configuration is trivial. Go to VMware Add Storage Wizard, select Network File System, then point to your NetApp filer and specify your volume path. Additionally NetApp recommends to tune NFS heartbeat parameters. Go to Host Configuration – Advanced Settings – NFS and for ESX 3.0 hosts change:

NFS.HeartbeatFrequency to 5 from 9
NFS.HeartbeatMaxFailures to 25 from 3

For ESX 3.5 hosts change:

NFS.HeartbeatFrequency to 12
NFS.HeartbeatMaxFailures to 10

There are much more information and tuning parameters that you might want to read about. Find some time to look through TR-3428 in case you need some clarifications or additional info.


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4 Responses to “NetApp thin provisioning for VMware”

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