Phill Bullinger and his staff from Western Digital presented at Storage Field Day 15 (SFD15) on a number of their enterprise products including Tegile and IntelliFlash but the one that caught my interest was their ActiveScale object store acquired from Amplidata back in 2015.
ActiveScale is an onprem, object storage system that provides cloud-like economics for customer data.
ActiveScale Hardware
ActiveScale systems can both scale up and scale out within a single site. ActiveScale systems have both storage and system nodes. Storage nodes perform erasure coding and System nodes are control points and metadata managers for the object store.
ActiveScale comes in two appliance configurations that contain both storage and system nodes and storage required. The two appliances are:
- ActiveScale P100 is a 7U 720TB pod system and A full rack of P100s can read 8GB/sec and can have 17-9s data availability. The P100 can scale up to 2.1PB in a single rack and up to 18PB in the same namespace. The P100 is a higher performing solution with better performing storage and system nodes
- ActiveScale X100 is a 42U rack scale solution that holds up to 588 12TB drives or 5.8PB per rack. The X100 can scale up to 9 racks or 52PB in the same namespace. The X100 is a denser configuration with only 6 storage nodes and as such, has a better $/GB than the P100 above.
As WDC is both the supplier of the ActiveScale appliance and a supplier of disk storage they can be fairly aggressive with pricing on appliance systems.
Data integrity in ActiveScale
They make a point of saying that ActiveScale object metadata and data are stored separately. By separating data and metadata, they claim to be more resilient to system failures. Object metadata is 3 way replicated, in a replicated database, residing in system nodes. Other object systems often store metadata and object data in the same way.
Object data can be erasure coded. That is, object data is chunked, erasure coding protected and then spread across multiple disk drives for data protection. ActiveScale erasure coding is called BitSpread. With BitSpread customers identify the number of disk drives to spread object data across and the number of drive failures the system should recover from without data loss.
A typical BitSpread configuration splits object data into 18 chunks and spreads these chunks across storage columns. A storage column is from 6-18 storage nodes. There’s no pre-allocated space in BitSpread. Object data chunks are allocated to disk storage based on current capacity and performance of the system, within redundancy constraints.
In addition, ActiveScale has a background task called BitDynamics that scans erasure coded chunks and does a mathematical health check on the object data. If a chunk is bad, the object data chunk can be recovered and re-erasure coded back to proper health.
WDC performance testing shows that BitDynamics has 0 performance degradation when performing re-erasure coding. Indeed, they took out 98 drives in an ActiveScale cluster and BitDynamics re-coded all that data onto other disk drives and detected no performance impact. No indication how long re-encoding 98 disk drives of data took nor the % of object store capacity utilization at the time of the test but presumably there’s a report someplace to back this up
Unlike many public cloud based object storage systems, ActiveScale is strongly consistent. That is object puts (writes) are not responded back to the entity doing the put, until the object metadata and object data are properly and safely recorded in the object store.
ActiveScale also supports 3 site erasure coding. GeoSpread is their approach to erasure coding across sites. In this case, object metadata is replicated across 3 system nodes across the sites. Object data and erasure coded information is split into 20 chunks which are then spread across the three sites. This way if any one site goes down, the other two sites have sufficient metadata, object data chunks and erasure coded information to reconstruct the data.
ActiveScale 5.2 now supports asynch replication. That is any one ActiveScale cluster can replicate to any other ActiveScale cluster located continent distances away.
Unclear how GeoSpread and asynch replication would interact together, but my guess is that each of the 3 GeoSpread sites could be asynchronously replicated to 3 other sites for maximum redundancy.
Both GeoSpread and ActiveScale replication impact performance, depending on how far the sites are from one another and the speed and bandwidth of the links between sites.
ActiveScale markets
ActiveScale’s biggest market is media and entertainment (M&E), mostly used for media archive or tape replacement/augmentation. WDC showed one customer case study for the Montreaux Jazz Festival, which migrated 49 years of performance videos up to ActiveScale and can now stream any performance, on request, without delay. Montreax media is GeoSpread across 3 sites in France. Another option is to perform transcoding on the object media in realtime and stream the transcoded media.
Another large market is Bio/Life Sciences. Medical & biological scanners are transitioning to higher resolution scans which take more data space. And this sort of medical information needs to be kept a long time
Data analytics on ActiveScale
One other emerging market is data analytics. With the new S3A (S3 adapter), Hadoop clusters can now support object storage as a 2nd tier. One problem with data analytics is that they have lots of data and storing it in triplicate, costs an awful lot.
In big data world, datasets can get very large very quickly. Indeed PB sizes data sets aren’t that unusual. And with triple replication (in native HDFS). When HDFS runs out of space you have to delete data. Before S3A, the only way you could increase storage you had to scale out (with compute and storage and networking) in order to add capacity.
Using Hadoop’s S3A, ActiveScale’s can provide cold archive for data analytics. From a Hadoop user/application perspective, S3A ActiveScale storage looks like just another directory under HDFS (Hadoop Data File System). You can run MapReduce or other Hadoop application directly against object buckets. But a more realistic approach is to move inactive or cold data from an disk resident HDFS directory to a S3A directory
HDFS and MapReduce are tightly coupled and were designed to have data close to where computation happens. So, as long as the active data or working set data is on HDFS disk storage or directly in memory the rest of the (inactive) data could all be placed on S3A object storage. Inactive data is normally historical data no longer being actively analyzed while newer data would be actively analyzed. Older, inactive data can be manually or automatically archived off to S3A. With HIVE you can partition your database to have active data in HDFS disk storage and inactive data in S3A.
Another approach is if the active, working set data can all fit directly in memory then the data can reside on S3A object storage. This way the data is read from S3A storage into memory, analyzed there and output be done back to object store or HDFS disk. Because the data is only read (loaded) once, there’s only a minimal performance penalty to use S3A storage.
Western Digital is an active contributor to Hadoop S3A and have recently added performance improvements to S3A, such as better caching, partial object reading, and core XML performance tuning options.
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If your interested in learning more about Western Digital ActiveScale, check out the videos referenced earlier and their website.
Also you may be interested in these other posts on the WD sessions at SFD15:
The A is for Active, The S is for Scale by Dan Firth (@PenguinPunk)
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