DataCore Software has developed another exciting new feature extending the arsenal of enterprise features already present within SANsymphony-V. This new feature serves to enhance the performance of random write workloads which are among the most costly operations that can be performed against a storage system. The new Sequential Storage feature will be available in SANsymphony™-V10 PSP1 scheduled for release this month.
As applications drive storage system I/O, DataCore’s high-speed caching engine improves virtual disk read performance. The cache also improves write performance, but its flexibility is limited due to the need to destage data to persistent storage. In many environments the need to synchronize write I/O with back-end storage becomes the limiting factor to the performance that can be realized at the application level; hence the purpose of this development.
- Physical head movement across the surface of the rotating disk
- RAID-5 reads to calculate parity data
- Write amplification inherent to Flash and SSD devices
Sequential Storage changes the way SANsymphony-V stores data written to the virtual disks by:
- Storing all writes sequentially
- Coalescing writes to reduce the number of I/Os to back-end storage
- Indexing the sequential structure to identify the latest data for any given logical block address
- Directing reads to the latest data for a block using this index
- Compacting data by copying it and removing blocks that have been rewritten
Now the part everyone is waiting for – the performance numbers. There are three main states to consider from a performance perspective:
- Base – the underlying level of performance that can be achieved with a 100% random write workload, without Sequential Storage enabled.
- Maximum – the performance that can be achieved with a 100% random write workload, with Sequential Storage enabled but without compaction active.
- Sustained – the performance that can be sustained with a 100% random write workload, with Sequential Storage enabled and with compaction active.
| Base I
|Maximum IOPS||Sustained IOPS|
|Linear 20 GB volume, SATA WDC 1 TB drive||327||19,500||11,000|
|Linear 20 GB volume, SSD 840 EVO 250 GB Pool||10,000||62,000||36,000|
|Mirrored 100 GB volume, PERC H-800 RAID-5 Pool||860||67,000||40,000|
The above results highlight 3 key observations:
- Significant acceleration (>30x improvement) of low-cost SATA disks for random write loads is possible. In fact in this particular test with DataCore, the resulting sustained performance of 11,000 IOPS actually exceeded that of a conventional Solid State Disk which ran at 10,000 IOPS.
- The Solid State Disk also displayed improved performance going from 10,000 IOPS to 36,000 IOPS (>3x improvement).
- Write intensive RAID-5 workloads displayed the greatest amount of improvement from 860 IOPS to 40,000 IOPS (>45x improvement).
DataCore’s Sequential Storage capability aims to address a limitation every storage system experiences to some extent. Random writes not only severely impact application performance within mechanical systems such as magnetic disks, they can also drastically reduce the performance and shorten the lifespan of SSD/flash based devices because of the write amplification effects produced from the write I/O pattern (see this publication for more detail). You can expect this feature along with many others in SANsymphony™-V10 PSP1 due out later this month.