Summary OSD+s are enhanced object‐based storage devices (OSDs) able to deal with both data and metadata operations via data and directory objects, respectively. So far, we have focused on designing and implementing efficient directory objects in OSD+s. This paper, however, presents our work on also supporting data objects and describes how the coexistence of both kinds of objects in each OSD+ is profited to efficiently implement data objects and to speed up some common file operations. We compare our OSD+‐based Fusion Parallel File System (FPFS) with Lustre and OrangeFS through different microbenchmarks and HPCS‐IO scenarios. Results show that FPFS provides a throughput up to 37× better than Lustre and up to 95× better than OrangeFS for metadata workloads. FPFS also provides 34% more bandwidth than OrangeFS for data workloads and competes with Lustre in data writes. Results also show serious scalability problems in Lustre and OrangeFS that limit their performance.

This paper presents two mechanisms that can significantly improve the I/O performance of both hard and solid-state drives for read operations: KDSim and REDCAP. KDSim is an in-kernel disk simulator that provides a framework for simultaneously simulating the performance obtained by different I/O system mechanisms and algorithms, and for dynamically turning them on and off, or selecting between different options or policies, to improve the overall system performance. REDCAP is a RAM-based disk cache that effectively enlarges the built-in cache present in disk drives. By using KDSim, this cache is dynamically activated/deactivated according to the throughput achieved. Results show that, by using KDSim and REDCAP together, a system can improve its I/O performance up to 88% for workloads with some spatial locality on both hard and solid-state drives, while it achieves the same performance as a ‘regular system’ for workloads with random or sequential access patterns.

Management of directories with millions of files, accessed by thousands of clients at the same time, is a problem recently identified in HPC environments. This paper introduces an OSD+-based technique to deal with those directories. We use directory objects in OSD+ devices for dynamically distributing a huge directory among several servers. Directory objects work independently, achieving good performance and scalability. Experiments show that, by using just 8 OSD+s and Ext4, FPFS is able to create, stat and delete more than 70,000, 120,000 and 37,000 files per second, respectively. With ReiserFS, these numbers are 118,000, 97,000 and 67,000. Experiments, however, have produced unforeseen results too. While distribution is beneficial when a huge directory is accessed by many clients, it can also downgrade the performance when several huge directories are concurrently accessed by a few clients.

We present the design and implementation of both an enhanced type of OSD device, the OSD+ device, and a metadata cluster based on it. OSD+s support data objects and directory objects. A directory object stores file names and attributes, and supports metadata--related operations. OSD+s profit the directory implementation and features of the underlying file systems used by the storage nodes, achieving a great flexibility, simplicity and small overhead. By using OSD+ devices, we show how a metadata cluster can effectively be managed by all the servers in a system, improving the performance, scalability and availability of the metadata service. The performance of our new metadata cluster has been evaluated and compared with Lustre's. The results show that our proposal obtains a better throughput than Lustre when both use a single metadata server, easily getting improvements of more than 60--80\%, and that the performance scales with the number of OSD+s.

We present a framework for simulating the performance obtained by different I/O system mechanisms and algorithms at the same time, and for dynamically turning them on and off to improve the overall system performance. A key element of this framework is the the design and implementation of a virtual disk inside the Linux kernel. Our virtual disk creates a virtual block device which is able to simulate any hard drive with a negligible overhead, without interfering with regular I/O requests. We describe the potential of our proposal in REDCAP, a RAM-based disk cache which is dynamically activated/deactivated according to the throughput achieved. The results show that, by using our virtual disk, REDCAP obtains its maximum possible improvements: up to 80% for workloads with some spatial locality, and the same performance as a ''normal system" for workloads with random or large sequential reads.

Achieving high performance for out-of-core applications typically involves explicit management of the movement of data between the disk and the physical memory. We are developing a programming environment in which the different levels of the memory hierarchy are handled efficiently in a unified transparent framework. In this paper, we present our experiences with implementing efficient non-collective I/O (GPCIO) as part of this framework. As a generalization of the Remote Procedure Call (RPC) that was used as a foundation for the Sun NFS system, we developed a global procedure call (GPC) to invoke procedures on a remote node to handle non-collective I/O. We consider alternative approaches that can be employed in implementing this functionality. The approaches are evaluated using a representative computation from quantum chemistry. The results demonstrate that GPC-IO achieves better absolute execution times, strong-scaling, and weak-scaling than the alternatives considered.

Active Storage provides an opportunity for reducing the amount of data movement between storage and compute nodes of a parallel filesystem such as Lustre, and PVFS. It allows certain types of data processing operations to be performed directly on the storage nodes of modern parallel filesystems, near the data they manage. This is possible by exploiting the underutilized processor and memory resources of storage nodes that are implemented using general purpose servers and operating systems. In this paper, we present a novel user-space implementation of Active Storage for Lustre, and compare it to the traditional kernel-based implementation. Based on microbenchmark and application level evaluation, we show that both approaches can reduce the network traffic, and take advantage of the extra computing capacity offered by the storage nodes at the same time. However, our user-space approach has proved to be faster, more flexible, portable, and readily deployable than the kernel-space version.

This paper describes the foundation, design, implementation, and evaluation of DualFS, a new high-performance journaling file system which has the same consistency guarantees as traditional journaling file systems but a greater performance. DualFS places data and metadata in different devices (usually, two partitions of the same storage device) and manages them in very different ways. The metadata device is organized as a log-structured file system, whereas the data device is organized as groups. The new design allows DualFS not only to recover the consistency quickly after a system crash, but also to improve the overall file system performance. We have evaluated DualFS and we have found that it greatly reduces the total I/O time taken by the file system in most workloads as compared to other file systems (Ext2, Ext3, ReiserFS, XFS, and JFS). The work carried out has also allowed us to draw some lessons which ought to be taken into account when implementing new file systems

In this paper we introduce DualFS, a new high performance journaling file system that puts data and meta-data on different devices (usually, two partitions on the same disk or on different disks), and manages them in very different ways. Unlike other journaling file systems, DualFS has only one copy of every meta-data block. This copy is in the meta-data device, a log which is used by DualFS both to read and to write meta-data blocks. By avoiding a time-expensive extra copy of meta-data blocks, DualFS can achieve a good performance as compared to other journaling file systems. Indeed, we have implemented a DualFS prototype, which has been evaluated with microbenchmarks and macrobenchmarks, and we have found that DualFS greatly reduces the total I/O time taken by the file system in most cases (up to 97%), whereas it slightly increases the total I/O time only in a few and limited cases.