It now last for years and it seems to get even bigger with time: Storage needs are more important than before. You can think of it in terms of capacity, financial or administrative needs, It remains true.
Differents vendors have plenty of solutions to help you build your SAN, but most of those solutions are based on the very same technologies. I would like to give a spotlight to a different solution based on a different technology: EtherDrives and ATA over Ethernet.
Not long ago it was considered a minor option but is has nowadays a growing popularity.
The increasing power and speed of internet and PCs, the constantly moving needs, the spread of virtualisation and server consolidation… This all turns admins jobs into a mess when it comes to build, deploy and maintain a storage architecture, keeping peace of mind and ease of use.
There are quite a lot of solutions sold by known vendors. Almost all of them are based on two legacy technologies supposed to be THE way to go if you want an efficient SAN architecture:
- Fiber Channel SAN
- iSCSI SAN
Truely those technologies can do a lot, and did. But nowadays with growth of the storage needs, and the obligation for entreprises to reduce costs involved, we can ask ourselves: Do those legacy tehcnologies still meet the requirements: Robustness, Simplicity, Scalability and affordability.
Both FC and iSCSI are complex and expensive standards, so we can answer, no they don’t fit as well as they did.
A very insteresting alternative is AoE: ATA over Ethernet.
AoE is a technology allowing to export a storage device (block device) through the network layer: a SAN protocol. This solution differs from others in many aspects. Those aspects helps us reach the goals we previously exposed.
AoE, wide open.
The first reason, and the one that made me take a look at it, is that AoE is open-source. Why is it that important? For all the reasons that makes opensource software, a high quality, long-life and secure software. Developped and supported by Coraid, the ATA over Ethernet technology has free implementations for its client part (initiator) as well as on the server part (target). Indeed Coraid, contributed in Linux kernel with the integration of its own aoe driver. So Linux hosts are natively capable of integrating a SAN network based on AoE. It is also good to note that windows implementations are available as free or as non-free softwares . Looking at the target side, Coraid sells appliances embedding more and more featured, and offering more and more management and deployement facalities. There are also a number of open-sources projects allowing to export block devices throught AoE. The most popular is vblade, as it is shipped in packages mamangers of most moderns Linux distro. However, I do not consider vblade as the best option for building opensource AoE SAN. Other projects like ggaoed ou qaoed have similar performances and a more interresting approach (IMHO).
Simple is beautiful.
If you ever had to manage serious SAN, you may know that simplicity *IS* a feature. And when it comes to simplicty AoE just kicks any other serious competitor! Looking at the specifications documents of AoE is a perfect illustration: It fits in a dozen of pages where iSCSI needs more than two hundred (maybe a reason why there are so few free implementation of iSCSI). Of course this is just theorical documents but you can find this difference in many other levels:
When deploying an Ethernet SAN environment you can rely on your well known Gigabit network. You probably already know ethernet very well, don’t you? In this case it will be the efficient basis for your storage area, whereas if using iSCSI or Fiber networks you will have to buy costly hardware (HBAs, FC switch etc…) and spend time learning new concepts (if learning is always a good thing, spending time to do so is not always possible). AoE offers you to capitalise experience by relying on well known, robust and cost effective hardware. I personnaly already deployed several types of SAN, and I know that one the the most critical part of this kind of deployment is High Availability. Here too, Ethernet SAN simplicity helps a lot! In SAN world, when you talk about HA, you think “multipathing”. iSCSI and FC gain multipathing through an additionnal software layer:
- a daemon (multipathd on Linux) for FiberChannel
- a network driver allowing to create EtherChannels (or bonding) for iSCSI.
In both cases setup can quickly become tricky and require additionnal configuration on tiers network equipements. Actually you may end up with a layer that brings complexity and can make your admins’ life really harder, whereas it was supposed to bring them peace of mind. With AoE it all comes out of the (Coraid) box. High Availability is embedded in the aoe driver on the initiator side. On the target side, Coraid also embed this feature without any configuration. All you have to do is to plug several interfaces to several independant switches… and you got it: the precious HA. Icing on the cake:configuring HA (can we really call this configure?) also brought you network load-balancing. Please note that, while Coraid etherDrives all come with this feature, free implementations of AoE target are not equals. For example the most popular one (vblade) do not benefit from this feature and so requires you use bonding configuration. Fortunately ggaoed and qaoed offer that great feature.
A rising technology
If AoE by itself exists for many years now, it appears to have grown in terms of popularity lately in the world of industry. This is certainly a side effect of the efforts made by Coraid to improve their products. During lasts two years, they have added new categories of aplliances, bringing needed features like, ease of management, monitoring, replication solutions: the whole SAN admin toolkit.
As a consequence, big players of the virtualisation market started to integrated AoE in their management strategy. Today you can use VMWare ESX or Citrix XenServer with AoE storage to achieve an efficient server virtualisation. Of course free virtualisation plateform like Xensource, XCP or KVM may also benefit from AoE storage. Some free lifecycle tools even have support for AoE (convirt for example).
Conclusion.
The IT world is full of paradigms, sometimes spreaded by vendors, that once were true, but are no longer. The idea that stable and efficient SAN can only rely on FC or iSCSI is one of them. This document from Coraid propaganda exposes their reasons that makes AoE a competitive solution. Of course you can say this is just propaganda, but based on my own experience using AoE, iSCSI and FC fabrics, I can only aggre with what’s written there:
In short AoE is fast, AoE is simple, AoE is much cheaper than its direct competitors.
Leave a Reply