Cache Acceleration Software

CAS entered Intel's product line following Intel's August 2012 acquisition of Nevex Virtual Technologies, a Canadian startup.^[4] Intel rebranded the Nevex CacheWorks product as Intel Cache Acceleration Software with the release of version 2.0 in December 2012.^[5] Intel CAS was available in three variants: Windows Enterprise, Windows Workstation, and Linux.^[4]

CAS for Windows was an application-aware file-based cache that could be tuned by system administrators. It integrated with the operating system's buffer cache, creating a multi-tier cache architecture.^[5] CAS was also aware of some virtualization technologies such as vMotion, maintaining a hot SSD cache during VM migration.^[6]

CAS worked with enterprise-class Intel SSD products, such as the DC S3700 SATA drives and the DC P3700 NVMe PCI Express devices, as well as cache devices across SANs.^[4] Intel CAS for Linux consisted of a GPL-licensed loadable kernel module paired with a closed-source user-space administration tool. The Linux version supported CentOS, Red Hat Enterprise Linux, and SUSE Linux Enterprise Server.^[6] The Windows Enterprise version supported 64-bit Windows Server 2008 R2 SP1 and Windows Server 2012 R2, while the Windows Workstation version supported 64-bit Windows 7, 8.1, and 10.^[4]

A workstation version, called CAS-W, was announced in September 2013 by Dell under an exclusive agreement to offer CAS-W only for Dell Precision workstations.^[7][8]

In 2018, Intel open-sourced the Linux version of CAS, creating the Open CAS project. Open CAS Linux has the same features and capabilities as the former Intel CAS for Linux, but is distributed and implemented differently. Both Intel CAS for Linux and Intel CAS for Windows (the proprietary versions) reached end-of-life in 2023. Intel recommends users transition to Open CAS, which can be used with no license fee.^[9]

At the core of Open CAS is the Open CAS Framework (OCF), a high-performance block storage caching meta-library written in C. OCF is entirely platform- and system-independent, accessing system APIs through user-provided environment wrapper layers. It is designed to be embedded into other software stacks rather than compiled as a standalone library.^[10][11]

OCF serves as the foundation upon which adapter implementations are built for specific platforms. The two primary adapters are Open CAS Linux and the SPDK OCF block device.^[2]

Open CAS Linux provides kernel adapters for OCF, implementing a complete caching solution for Linux operating systems. It installs as a kernel module into the GNU/Linux operating system, providing a cache solution that is transparent to users and applications and requires no storage migration or application changes.^[3]

Open CAS Linux accelerates applications by caching active ("hot") data from slower backend block devices (such as HDDs or networked storage) to local high-performance flash media (such as NVMe SSDs or Intel Optane SSDs), positioning the cache as close as possible to the CPU to minimize storage latency.^[3]

Open CAS also provides an OCF adapter for the Storage Performance Development Kit (SPDK), enabling high-performance caching-aware applications built with SPDK. The SPDK OCF block device is independent from Open CAS Linux, implementing a different type of adapter while still utilizing the shared OCF core.^[2]

Open CAS Linux supports multiple caching modes:^[3]

• Write-through — data is written simultaneously to both the cache and the backend device, ensuring data consistency
• ライトバック— データはまずキャッシュに書き込まれ、その後バックエンドデバイスにフラッシュされるため、書き込みパフォーマンスが向上します。
• ライトアラウンド― 書き込み操作はキャッシュをバイパスしてバックエンドデバイスに直接アクセスするため、書き込み負荷の高いワークロードによるキャッシュ汚染を防ぐ。
• 書き込み専用— 書き込み操作のみがキャッシュされます
• パススルー— キャッシュを完全にバイパスするI/O方式。メンテナンスや診断に役立ちます。

CASはワークロードの分類と階層化をサポートしており、管理者はブロックサイズ、ファイル、ディレクトリ/パス、メタデータによってI/Oを分類して、柔軟なキャッシュチューニングを行うことができます。^{[ 3 ]}

Open CASプロジェクトには、Kubernetes環境にOpen CASをデプロイするためのコンテナストレージインターフェース（CSI）ドライバ（open-cas-csi）が含まれており、カーネルモジュール管理オペレータを使用してクラスタノード全体でカーネルモジュールのビルドを管理します。^{[ 12 ]}