IBM Systems Journal
The HP AutoRAID hierarchical storage system
ACM Transactions on Computer Systems (TOCS) - Special issue on operating system principles
Summary cache: a scalable wide-area web cache sharing protocol
IEEE/ACM Transactions on Networking (TON)
Space/time trade-offs in hash coding with allowable errors
Communications of the ACM
Proceedings of the 2003 ACM SIGMOD international conference on Management of data
The Conquest file system: Better performance through a disk/persistent-RAM hybrid design
ACM Transactions on Storage (TOS)
File system design for an NFS file server appliance
WTEC'94 Proceedings of the USENIX Winter 1994 Technical Conference on USENIX Winter 1994 Technical Conference
FlexVol: flexible, efficient file volume virtualization in WAFL
ATC'08 USENIX 2008 Annual Technical Conference on Annual Technical Conference
Optimal file allocation in multi-level storage systems
AFIPS '73 Proceedings of the June 4-8, 1973, national computer conference and exposition
Migrating server storage to SSDs: analysis of tradeoffs
Proceedings of the 4th ACM European conference on Computer systems
Cost effective storage using extent based dynamic tiering
FAST'11 Proceedings of the 9th USENIX conference on File and stroage technologies
Hystor: making the best use of solid state drives in high performance storage systems
Proceedings of the international conference on Supercomputing
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Relative to traditional hard disk drives (HDDs), solid state drives (SSDs) provide a very large number of I/Os per second, but they have limited capacity. From a cost-effectiveness perspective, SSDs provide significantly better random I/O throughput per dollar than a typical disk, but the capacity provided per dollar spent on SSDs limits them to the most demanding of datasets. Traditionally, Data ONTAP® storage aggregates have been provisioned using a single type of disk. This restriction limits the costeffectiveness of the storage pool to that of the underlying disks. The Hybrid Aggregates project within the Advanced Technology Group (ATG) explored the potential to combine multiple disk types within a single aggregate. One of the primary goals of the project was to determine whether a hybrid aggregate, composed of SSDs (for their cost-effective performance) and Serial-ATA (SATA) disks (for their cost-effective capacity), could simultaneously provide better cost/performance and cost/throughput ratios than an all Fibre-Channel (FC) solution. The project has taken a two-pronged approach to building a prototype system capable of supporting hybrid aggregates. The first part of the project investigated the changes necessary for Data ONTAP RAID and WAFL® layers to support a hybrid aggregate. This included propagating disk-type information to WAFL, modifying WAFL to support the allocation of blocks from a particular storage class (i.e., disk type), and repurposing the existing writeafter- read and segment-cleaning infrastructure to support the movement of data between storage classes. The second part of the project examined potential policies for allocating and moving data between storage classes within a hybrid aggregate. Through proper policies, it is possible to automatically segregate the data within the aggregate such that the SSD-backed portion of the aggregate absorbs a large fraction of the I/O requests, leaving the SATA disks to contribute capacity for colder data. This paper describes the implementation of the Hybrid Aggregates prototype and the policies for automatic data placement and movement that have been evaluated. It also presents some performance results from the prototype system.