A closer look at Dot Hill Systems

Dot_Hill_Logo_1000_8.2_copyLast week, I was at our VMware Partner Exchange event in Las Vegas. Apart from my own break-out session on vSphere 5.1 storage features, I wanted to catch up with a number of our partner vendors who are doing cool things in the storage space. One of these vendors is Dot Hill, a company from Longmont, Colorado, who have been making storage arrays for a considerable amount of time now, but one which does not seem to get a huge amount of exposure. I caught up with Matt Alsip, the Technical Marketing Manager at Dot Hill, to put my customary set of questions to him about their products and how their arrays integrate with vSphere.

My first question was about the VMware HCL entries for Dot Hill. It seems that there are both R/Evolution arrays and AssuredSAN arrays. Matt explained that the R/Evolution is the older product name, and that AssuredSAN is the new umbrella name for the current set of Dot Hill arrays. However Dot Hill’s latest array, the Pro 5000, doesn’t yet appear on our HCL. Matt stated that this was imminent, and we got into discussing the features of this new array.

Pro 5000 Hybrid Array

First off, the Pro 5000 is a hybrid array, meaning it contains a combination of SSD & spinning HDD. It can be purchased with a combination of SSD/SAS or SSD/SAS/Near line SAS. It is also an Active/Active array, meaning that all paths to the LUN are active, allowing customers to use VMware’s Round Robin path policy. Dot Hill have what they call a virtualization stack built into the storage array. This means that the RAID sets that are created on the array are virtualized which in turn enables tiering capabilities on the array. If a disk block becomes ‘hot’ on one tier (RAID set) it can be moved to a higher performance storage tier (SSD). If the data in that block becomes cold through lack of access, it can seamlessly be moved back to SAS layer. Matt explained that this is quite a unique feature for Dot Hill in that this tiering operation is done is real-time rather than batch processing. It can be done on the fly without impacting the data stream. He also explained that up to 20 pages can be moved between tiers every 5 secs. A page equates to 4MB, so this is moving 80MB every 5 seconds to ensure that the most optimal storage blocks reside in the SSD tier.

While this sounds really neat, I need to call out an interoperability issue between Storage DRS and SIOC with tiered storage. If you are not familiar with the considerations in this context, go and check out Frank Denneman’s excellent white paper on the topic. Dot Hill is in the process of establishing Best Practices for the Pro 5000 in environments that utilize Storage DRS. Watch this space.


The 5000 supports block storage only (no NAS) and the controllers on the array can support Fiber Channel or 10Gb iSCSI. There is currently no SAS interface for the 5000, but this is on the road map.  There is no support for FCoE at this time.

Hardware Configuration

The minimum configuration for a 5000 series  array is two x 2U chassis, giving a total of 4U.   The 5000 series offers 5x9s or 99.999% availability. In a single 2U chassis, there are two controllers & everything is hot swappable. The array is designed to be a scale-up solution, not a scale out one. A single 5000 array can support up to 10 expansion chassis (JBODs). That is a total of 240 drives.

Array Features

The 5000 supports AssuredCopy for full volume copes & AssuredSnap for point in time copies. AssuredRemote, Dot Hill’s remote replication feature, is also supported. Dot Hill also have an SRA (Replication Adapter) to allow their arrays to integrate with SRM, VMware’s Site Recovery Manager product, for Disaster/Recovery scenarios. This is in the process of being certified right now.

VAAI Support

All of the block primitives are supported, which is always nice to see.

Array Management

Dot Hill have a brand new management interface which includes lots of filtering and searching. However the UI only manages a single array and Dot Hill do not have plugins to either the vSphere C# or web client, which is a shame. However Matt has taken this on-board and is going to discuss this internally as a possible item to add to their road map.


The last question I asked Matt was about how Dot Hill differentiates itself from the plethora of other storage vendors in this space. What is so unique about the 5000, and why should potential customers consider this over other arrays on the market? (this is my favorite question by the way). Matt stated that Dot Hill has the staying power and the legs that many other companies do not have, with almost 550,000 units shipped. In case you haven’t guessed it, Dot Hill are an OEM for HP who sell their arrays as the MSA. Matt also called out their new secret sauce of tiering and their ability to move data in real-time from tier to tier. Finally, Matt states that their 5x9s availability makes them a very good player in the mid-range storage market.

In conclusion, I will say that Dot Hill seem to have done a lot of things well from a vSphere integration perspective. Full VAAI block primitive support and an SRA for SRM bodes very well. One thing I did notice is that there is no dedupe or compression technology with this array, and the fact that the management console is not integrated into vSphere, and only works on a 1:1 basis with the array, is perhaps something which could be considered by Dot Hill going forward. But overall, a nice fit in my opinion.

[Update] Dot Hill were acquired by Seagate in October 2015. More here.