In computer storage, NetApp filer, known also as NetApp Fabric-Attached Storage (FAS), is NetApp's network attached storage (NAS) device. A FAS is an enterprise-class Storage area network (SAN), as well as a networked storage appliance. It is able to serve storage over the network using file-based protocols such as NFS, CIFS, FTP, TFTP, and HTTP. Filers can also server data over block-based protocols such as Fibre Channel (FC) and iSCSI.^[1] It is equipped with large disk arrays.

Most other large storage vendors' filers are usually commodity computers with an operating system such as Microsoft Windows Storage Server or tuned Linux. NetApp filers use highly customized commodity hardware and proprietary Data ONTAP operating system, both designed specifically for storage-serving purposes.

All filers have battery-backed NVRAM, which allows them to commit writes to stable storage quickly, without waiting on disks. Early filers used to connect to external disk enclosures via SCSI, but the current ones use FC protocol. Those disk enclosures (shelves) support FC hard disk drives, as well as parallel ATA and serial ATA ones.

Two filers are often organized in a high-availability cluster via a private high speed link, either FC or InfiniBand. These clusters, can be grouped together under a single namespace when running the OnTap GX operating system.

Architecture

Most NetApp filers are servers actually customized computers, with Intel or AMD processors and based on PCI. Each Filer has a proprietary NVRAM adapter to log all writes for performance and to play the data log forward in the event of an unplanned shutdown. Two filers can be linked together as a cluster, although NetApp now uses the more correct term Active/Active. Data ONTAP implements a single proprietary file system called WAFL. When used for file storage, Data ONTAP acts as an NFS server and/or a CIFS server, serving files to both Unix-like systems and Microsoft Windows systems from the same file systems. This makes it possible for Unix and Windows to share files by the use of three qtree security styles: mixed, ntfs, and unix. Qtree stands for quota trees and allows for data segregation and management inside of volumes. Qtrees with the UNIX security style will preserve the standard UNIX permission bits, the NTFS security style will preserve NT ACLs found in the Windows environment, and the mixed security allow both to be used interchangeably (with some functionality loss).

Each filer model comes with a set configuration of processor, RAM and NVRAM, which cannot be expanded once purchased. With the exception of the FAS200 series and the FAS2020, the NetApp filers have at least one PCI based slot available additional network, tape and/or disk connections. In June, 2008 NetApp announced the Performance Acceleration Module (or PAM) to optimize the performance of random read intensive workloads. This optional card is inserted into a PCI slot and provides additional memory (or cache) between the disk and the filer RAM/NVRAM improving performance.

NetApp supports either SATA, Fibre Channel, or SAS disk drives, which are grouped 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). Multiple RAID Groups form an aggregate and then flexible volumes are created within the aggregate to actually store data that can be accessed by users. An alternative is "Traditional volumes" where one or more RAID groups form a single static volume. The advantage of flexible volumes is that many of them can be created on a single aggregate and resized at any time. Smaller volumes can then share all of the spindles available to the underlying aggregate. Traditional volumes and aggregates can only be expanded, never contracted. However, Traditional Volumes can (theoretically) handle slightly higher I/O throughput than Flexible Volumes (with the same number of spindles), as they do not have to go through an additional viritualisation layer to talk to the underlying disk.

WAFL is a robust versioning file system and as such provides snapshots, which allows end-users to see earlier versions of files in the file system. Snapshots appear in a hidden directory ~snapshot for Windows (CIFS) or .snapshot for Unix (NFS). Up to 255 snapshots can be made of any Traditional or Flexible volume. Snapshots are read only although Data ONTAP 7 provides the ability to make snapshots writable as "FlexClones".

Snapshots are implemented by tracking changes to disk blocks between snapshots, and can be created in seconds because Data ONTAP only needs to take a copy of the root inode in the filesystem. This is different from the snapshots provided by some other storage vendors in which every block of storage has to be copied, which can take many hours.

Snapshots are the basis for NetApp disk replication technology SnapMirror, which effectively replicates snapshots between two NetApp filers. Later versions of Data ONTAP introduced cascading replication, where one volume could replicate to another and then another etc. NetApp also offers a backup product based around replicating and storing snapshots, called SnapVault. Open Systems SnapVault allows Windows and UNIX hosts to backup data to a NetApp filer and store any filesystem changes in snapshots.

Data ONTAP also implements an option called "SyncMirror" where all the raid groups within an aggregate or traditional volume can duplicated to another set of hard disks, typically at another site via a Fibre Channel link. NetApp provides a "MetroCluster" option, that uses "SyncMirror" to provide a geo-cluster or active/active cluster between two sites up to 100 km apart.

Other product options include "SnapLock" which implements a "Write Once Read Many" functionality on magnetic disks instead of optical media, so that data cannot be deleted (even by the administrator) until it meets certain retention criteria.

NetApp also offers products for taking application consistent snapshots by coordinating the application and the NetApp Storage Array. This products support Microsoft Exchange, Microsoft SQL Server, Microsoft Sharepoint, Oracle, SAP and soon VMware ESX Server data. These products are part of the SnapManager suite.

Current limitations

Currently individual aggregates sizes (gross sizes, i.e. raid disks and file system overhead has to be subtracted from these numbers) are limited to a maximum of 8TB for FAS2020 models and 16TB for all other models; this has two impacts:

1. With the availability of larger drives (such as 1TB), the number of spindles (i.e. physical disks) within an aggregate becomes smaller and as a result I/O cannot be spread over as many disks, reducing performance.
2. Each Aggregate incurs a storage capacity overhead of approximately 11%. On systems with many aggregates this can add up to a substantial overall capacity loss that isn't available to the end-user.

Model history

This list is incomplete and omits some early models and most current models. Info taken from spec.org and netapp.com and storageperformance.org

SPECsfs with "*" is clustered result. SPECsfs are done is SPECsfs93, SPECsfs97 or SPECsfs97_R1. Check spec.org for more details.

References

See also

• Filer
• NetApp
• Write Anywhere File Layout (WAFL), for an innovative filer's filesystem