Saturday, August 15, 2009

Unified Storage with focus on NetApp and EMC

When you think of storage, you either think of SAN or NAS - depending on what your requirement is. What if it is both? The tendency is to think of both requirements as separate and hence the requirement is for two solutions. What if both of the requirements can be achieved with a single solution? Then comes "unified storage" into picture. Unified storage is no mystery except that the underlying storage array should be capable of serving both NAS and SAN clients.

Even though it was SUN that developed the original protocol for Network File System, it was NetApp that made it popular in storage world. NetApp pioneered the protocol and developed storage arrays based on NFS. The only file server competitor it had at that time was Auspex (if you care to remember). The names NetApp and Filer goes hand in hand when people usually refer to them. NetApp started adding block based protocol to its storage arrays not soon when it realized there is not much potential for growth in just the NAS segment. That was really a good move for storage admin who preferred to have both file-based and block-based protocols to be served from a single array- managing one device rather than two (or more). Maybe it was not a so good from a stability point (too many bugs!!). But soon, NetApp overcame the initial hiccups and made its storage devices and OS (DATA OnTAP) as robust as it was for NAS.

I don't think EMC needs an introduction to anyone in the Storage (or for that matter any field) field. If there is any company in the Storage Area making acquisitions like crazy, it would be EMC. It can also be credited for the poor integration of its acquisitions into its mainstream products. EMC is very well known for its block based products . It also has unified storage products serving both NAS and SAN.

Let us take a quick look at both of them and compare them for their capabilites, advantages and disadvantages for both NAS and SAN in their unified product line.

Disk virtualization was made popular byNetApp. With its aggregates spread across multiple disks and Ontap managing 4K block segments there would literally be no hot-spots on disks. When it initially came out with an aggregate limitation of 16TB, not many gave a second thought since 16TB seemed to be far off from what they use. But, with growing disk sizes, it is now a major problem bugging them and their customers to look at alternative solutions. The whole concept of disk-virtualization advantages are now gone as your can only have "x" number of disks in each aggregate and you will need to do a layout and maintian spreadsheets of what goes where. This may not be the case with every customer, but certainly with large customers they all face this everday problem of managing space.

EMC took its Clariion product and slapped couple of "heads" with Microsoft OS on them and started doing NAS with Celerra. I am not sure if this is really a good solution, especially when the OS hangs and you have to reboot controllers (or blades). Agreed that all controllers are redundant, this is still an issue. The N+1 architecture defines a fail-over hot-standby for all the remaining N controllers. This may seem to be a good thing until you realize what happens if more than one controller failover to the standby. In order for the standby to support failover for more than a single blade, each of the individual blades now have to be running at 1/N of their capacity. This does not seem right!! At least with NetApp, to support failover you just need to be running at 50%. Now, with 3 active blades, you have to be running at 33% and with 4 blades you have to stick to 25%. Even EMC is plagued with the familiar 16TB limitation, except that theirs is usable capacity while NetApp's is based on RAW capacity.

Both NetApp and EMC can serve NAS (NFS and CIFS) with the same degree robustness. But when it comes to SAN, in case of NetApp you just create another volume and then a lun and assign to host and you are done. But with EMC, you cannot use the same interface that you manage your NAS (Celerra) - you now have to use the Clariion interface to create the luns, and watchout for where you are creating. EMC cannot virtualize disk as NetApp does over a whole bunch of disks - rather they have to carve out luns from a set number of disks. And watchout for those 5 drives in the first DAE where the FLARE code resides. Your array and its configuration is now wholly dependent on these drives which is a RAID-5. So your entire array reliability and availability is as good as RAID-5.

Again, with NetApp you can use built in OS tools to manage multipathing in SAN whereas with EMC, you will have to purchase licensed powerpath. There are also lots of other software that you will need to manage and monitor storage performance that need to be purchased from both EMC and NetApp that you need to be aware of.

The scalability of NAS connectivity with NetApp is as simple as adding more Ethernet ports, but in Celerra you need to know what each blade configuration can provide - some models can support only few ethernet ports and if you need more you will have to do an upgrade to the next model. If you are involved in the decision to purchase, the last thing you want to do is to stand before management and ask for budget to upgrade the storage array you just bought few months ago. I would not want to be standing in those shoes!!

One of the major advantage of using NetApp over EMC as I see it, is the ability to resize volumes as and when required. With Celerra, that is not possible and you will have to do data migration to resize volumes - although EMC claims you can start off with a thinly provisioned volume, that is not going to help with volume resizing in any way.

And snapshots are just a snap with NetApp - be it a NAS volume or a SAN LUN. With EMC, you have to go through the snapview and/or cloning process (again through Clariion) and is not efficient and effective as it is a Copy on Write - which has a write penalty, while NetApp's snapshot is a true physical snapshot.

Where both companies are lagging is in HSM - Heirarchical Storage Management. EMC uses rainfinity, while NetApp does not even have one. NetApp's preferred one used to be VFM, which is no longer being offered (that's the last I know of). With both companies having 16TB limitations on volumes and not addressing it, and cannot even provide a solution for customers' pain points I believe they are not even listening to customers. Rather than starting a bidding war for DataDomain, why cannot they address the issues in their storage arrays? Maybe they don't care? Once you are locked into a vendor they know you will stick to them or else the loss is yours.

Recent technologies enables massive cluster file system with almost no limitations and have virtually all the features that the big boys have. Maybe it is time to let the big boys know that we don't care about them if they are not listening!!

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