A NetApp FAS is a computer storage product by NetApp running the ONTAP operating system; the terms ONTAP, FAS, AFF, and ASA are often used as synonyms. "Filer" is also used as a synonym although this is not an official name. There are several types of custom-built hardware appliances:
Fabric Attached Storage (FAS) - combine Serial Attached SCSI (SAS) SSDs and HDDs to provide a hybrid storage system optimized for capacity and cost-effectiveness; All-Flash FAS (AFF) - based on NVMe SSDs (TLC for extreme performance, or QLC for high-capacity) optimized for low-latency; All-Flash SAN Array (ASA) - built on top of the AFF platform, providing a high-performance block-only storage system.
ONTAP can provide network-attached storage (NAS) using file-based protocols such as NFS or SMB and object-based protocols such as S3, as well as service on a storage area network (SAN) using block-based protocols, such as SCSI over the Fibre Channel Protocol on Fibre Channel or on Fibre Channel over Ethernet (FCoE), iSCSI, and FC-NVMe. ONTAP-based systems that can serve SAN, file, and NAS protocols are called Unified ONTAP, AFF systems with ASA identity are called All-SAN.
Early FAS storage systems connected to external disk enclosures via parallel SCSI, while modern models () use SCSI over Fibre Channel and SAS.
While most large-storage systems are implemented with commodity computers with an operating system such as Microsoft Windows Server, VxWorks or tuned Linux, ONTAP-based hardware appliances use highly customized hardware and the proprietary Data ONTAP operating system with WAFL file system, all originally designed by NetApp founders David Hitz and James Lau specifically for storage-serving purposes. ONTAP is NetApp's internal operating system, specially optimized for storage functions at high and low levels.
All NetApp ONTAP-based hardware appliances have battery-backed non-volatile random access memory (NVRAM) or NVDIMM, which allows them to commit writes to stable storage more quickly than traditional systems with only volatile memory. Starting with AFF A800 NVRAM PCI card no longer used for NVLOGs, it was replaced with NVDIMM memory directly connected to the memory bus.
Implementers often organize two storage systems in a high-availability cluster with a private high-speed link, either Fibre Channel, InfiniBand, 10 Gigabit Ethernet, 40 Gigabit Ethernet or 100 Gigabit Ethernet. One can additionally group such clusters together under a single namespace when running in the "cluster mode" of the Data ONTAP 8 operating system.
Internal architecture
Modern NetApp FAS, AFF or ASA system consist of customized computers with Intel processors using PCI. Each FAS, AFF or ASA system has non-volatile random access memory, called NVRAM, in the form of a proprietary PCI NVRAM adapter or NVDIMM-based memory, to log all writes for performance and to play the data log forward in the event of an unplanned shutdown. One can link two storage systems together as a cluster, which NetApp (as of 2009) refers to using the less ambiguous term "Active/Active".
Hardware Each storage system model comes with a set configuration of processor, RAM, and non-volatile memory, which users cannot expand after purchase. With the exception of some of the entry point storage controllers, the NetApp FAS, ASA, and AFF systems usually have at least one PCIe-based slot available for additional network, tape and/or disk connections. In June 2008 NetApp announced the Performance Acceleration Module (or PAM) to optimize the performance of workloads that carry out intensive random reads. This optional card goes into a PCIe slot and provides additional memory (or cache) between the disk and the storage system cache and system memory, thus improving performance.
AFF All-Flash FAS, also known as AFF A-Series. Usually, AFF systems based on the same hardware as FAS but first one optimized and works only with triple-level cell (TLC) NVMe SSD on the back end while the second one can use HDD and SSD as a cache: for example, AFF A700 & FAS9000, A300 & FAS8200, A200 & FAS2600, A220 & FAS2700 use the same hardware, but AFF systems do not include Flash Cache cards. Also, AFF systems do not support FlexArray with third-party storage array virtualization functionality. AFF is a Unified system and can provide SAN & NAS data protocol connectivity, and in addition to traditional SAN & NAS protocols in FAS systems, AFF has block-based NVMe/FC protocol for systems with 32 Gbit/s FC ports. AFF & FAS use the same firmware image, and nearly all noticeable functionality for the end-user is the same for both storage systems. However, internally data is processed and handled differently in ONTAP. AFF systems, for example, use different Write Allocation algorithms as compared to FAS systems. Because AFF systems have faster underlying SSD drives, Inline data deduplication in ONTAP systems is nearly not noticeable (≈2% performance impact on low-end systems).
In February 2023, NetApp introduced a new AFF product line, code-named the C-Series. This platform uses NVMe SSD with quad-level cell (QLC) NAND flash and is aimed at competing with the QLC-based products already in the market from Pure Storage (specifically FlashArray//C). The C-Series has higher latency than typical AFF systems, at around 2-4 milliseconds compared to 500 microseconds on AFF using triple-level cell (TLC) media. However, the aim of the platform is to provide a lower price point for customers that might otherwise not choose all-flash systems.
ASA All-Flash SAN Array running ONTAP, and based on AFF platform thus inherits its features & functionalities, and data internally processed and handled the same as in AFF systems. All other ONTAP-based hardware and software platforms can be referred to as Unified ONTAP meaning they can provide unified access with SAN & NAS data protocols. ONTAP architecture in ASA systems is the same as in FAS & AFF, with no changes. ASA systems using the same firmware image as AFF & FAS systems. ASA is the same as AFF, and the only difference is in the access to the storage over the network with SAN protocols: ASA provides symmetric active/active access to the block devices (LUN or NVMe namespaces), while FAS systems continue to use ALUA for the block protocols. The original ASA platform was first announced in 2019 and re-launched in May 2023.
Storage NetApp uses either SATA, Fibre Channel, SAS or SSD disk drives, which it groups into RAID (Redundant Array of Inexpensive Disks or Redundant Array of Independent Disks) groups of up to 28 (26 data disks plus 2 parity disks). NetApp FAS storage systems which contain only SSD drives with installed SSD-optimized ONTAP OS called All-Flash FAS (AFF).
Disks FAS, ASA, and AFF systems are using enterprise-level HDD and SSD (i.e. NVMe SSD) drives with two ports, each port connected to each controller in an HA pair. HDD and SSD drives can only be bought from NetApp and installed in NetApp's Disk Shelves for FAS/AFF platform. Some shelves, such as the D4246, can be upgraded from a 6 Gbit/s Shelf into a 12 Gbit/s with an IOM-12 upgrade. Physical HDD and SSD drives, partitions on them, and LUNs imported from third-party arrays with FlexArray functionality considered in ONTAP as a Disk. In SDS systems like ONTAP Select & ONTAP Cloud, logical block storage like virtual disk or RDM inside ONTAP also considered as a Disk. Do not confuse the general term "disk drive" and "disk drive term used in ONTAP system" because, with ONTAP, it could be an entire physical HDD or SSD drive, a LUN, or a partition on a physical HDD or SSD drive. LUNs imported from third-party arrays with FlexArray functionality in HA pair configuration must be accessible from both nodes of the HA pair. Each disk has ownership on it to show which controller owns and serves the disk. An aggregate can include only disks owned by a single node, therefore each aggregate owned by a node and any objects on top of it, as FlexVol volumes, LUNs, File Shares are served with a single controller. Each controller can have its own disks and aggregates them where both nodes can be utilized simultaneously even though they not serving the same data.
ADP Advanced Drive Partitioning (ADP) can be used in ONTAP-based systems depending on the platform and use-case. ADP can be used only with native disk drives from NetApp Disk shelves, FlexArray technology does not support ADP. ADP also supported with third-party drives in ONTAP Select. This technique mainly used to overcome some architectural requirements and reduce the number of disk drives in ONTAP-based systems. There are three types of ADP: Root-Data partitioning; Root-Data-Data partitioning (RD2 also known as ADPv2); Storage Pool. Root-Data partitioning can be used in FAS & AFF systems to create small root partitions on drives to use them to create system root aggregates and, therefore, not to spend entire three disk drives for that purpose. In contrast, the bigger portion of the disk drive will be used for data aggregate. Root-Data-Data partitioning is used in AFF systems only for the same reason as Root-Data partitioning with the only difference that bigger portion of the drive left after root partitioning divided equally by two additional partitions, usually, each partition assigned to one of the two controllers, therefore reducing the minimum number of drives required for an AFF system and reducing waste for expensive SSD space. Storage Pool partitioning technology used in FAS systems to equally divide each SSD drive by four pieces which later can be used for FlashPool cache acceleration, with Storage Pool only a few SSD drives can be divided by up to 4 data aggregates which will benefit from FlashCache caching technology reducing minimally required SSD drives for that technology.
NetApp RAID in ONTAP
In NetApp ONTAP systems, RAID and WAFL are tightly integrated. There are several RAID types available within ONTAP-based systems: RAID 4 with 1 dedicated parity disk allowing any 1 drive to fail in a RAID group. RAID-DP with 2 dedicated parity disks allowing any 2 drives to fail simultaneously in a RAID group. RAID-TEC with 3 dedicated parity drives, allows any 3 drives to fail simultaneously in a RAID group. RAID-DP's double parity leads to a disk loss resiliency similar to that of RAID 6. NetApp overcomes the write performance penalty of traditional RAID-4 style dedicated parity disks via WAFL and a novel use of its nonvolatile memory (NVRAM) within each storage system. Each aggregate consist of one or two plexes, a plex consists of one or more RAID groups. Typical ONTAP-based storage system have only 1 plex in each aggregate, two plexes used in local SyncMirror or MetroCluster configurations. Each RAID group usually consists of disk drives of same type, speed, geometry and capacity. Though NetApp Support could allow a user to install a drive to a RAID group with same or bigger size and different type, speed and geometry for temporary basis. Ordinary data aggregates if containing more than one RAID group must have same RAID groups across the aggregate, same RAID group size is recommended, but NetApp allows to have exception in last RAID group and configure it as small as half of the RAID group size across aggregate. For example, such an aggregate might consists of 3 RAID groups: RG0:16+2, RG1:16+2, RG2:7+2. Within aggregates, ONTAP sets up flexible volumes (FlexVol) to store data that users can access.