Thursday, 6 October 2011

NetApp architecture

The NetApp architecture consist of hardware, Data ONTAP operating system and the network. I have already shown you a diagram of a common NetApp setup but now i will go into more detail.

NetApp have a number of filers that would fit into any company and cost, the filer itself may have the following
  • can be a Intel or AMD server (up to 8 dual core processors) 
  • can have dual power supplies 
  • can handle up to 64GB RAM and 4GB NVRAM (non-volatile RAM) 
  • can manage up to 1176GB storage 
  • has a maximum limit of 1176 disk drives 
  • can connect the disk shelves via a FC loop for redundancy 
  • can support FCP, SATA and SAS disk drives 
  • has a maximum 5 PCI and 3 PCI-express slots 
  • has 4/8/10GbE support 
  • 64bit support
The filer can be attached to a number of disk enclosures (shelves) which expands the storage allocation, these disk enclosures are attached via FC, as mentioned above the disk enclosures can support the following disks

FCP       These are fibre channel disks, they are very fast but expensive
SAS       Serial attached SCSI disks again are very fast but expensive , due to replace the FC disks
SATA    Serial ATA are slow disks but are cheaper, ideal for QA and DEV environments

One note to remember is that the filer that connects to the top module of a shelf controls (owns) the disks in that shelf under normal circumstances (i.e. non-failover).

The filers can make use of VIF's (Virtual Interfaces), they come in two flavors

Single-mode VIF

  • 1 active link, others are passive, standby links 
  • Failover when link is down
  • No configuration on switches

Multi-mode VIF

  • Multiple links are active at the same time 
  • Loadbalancing and failover 
  • Loadbalancing based on IP address, MAC address or round robin
  • Requires support & configuration on switches


I have already touched on the operating system Data ONTAP, the latest version is currently version 8 which fully supports grid technology (GX in version 7). It is fully compatible with Intel and AMD architectures and supports 64bit, it borrows the idea's from FreeBSD.

All additional NetApp products are activated via licenses, some require the filer to be rebooted so check the documentation.

Management of the filer can be accessed via any of the following
  • Telnet or SSH
  • Filerview (HTTP GUI)
  • System Manager (client software GUI)
  • Console cable
  • snmp and ndmp
Storage Terminology

When talking about storage you probably come across two solutions

NAS (Network Attached Storage)
   NAS storage speaks to a file, so the protocol if a file based one. Data is made to be shared examples are
  • NFS (Unix)
  • CIFS or SMB (Windows)
SAN (Storage Area Network)

SAN storage speaks to a LUN (Logical Unit Number) and accesses it via data blocks, sharing is difficult examples are
  • SCSI
  • iSCSI

There are a number of terminologies associated with the above solutions, I have already discussed some of them in my EMC section

CIFS servers makes data available via shares, a Unix server makes data available via exports
    Drive                     g  mapping/mounting
CIFS clients typically map a network drive to access data stored on a storage server, Unix clients typically mount the remote resource
Logical Unit Number , basically a disk presented by a SAN to a host, when attached it looks like a locally attached disk.
The machine that offers a disk (LUN) to another machine in other words the SAN
The machine that expects to see the disk (LUN) the host OS, appropriate initiator software will be required
One or more fibre switches with targets and initiators connected to them are referred to as a fabric. Cisco, McData and Brocade are well know fabric switch makers
See my EMC architecture section for more details
Host Bus Adapter, the hardware that connects the server or SAN to the fabric switches. There are also iSCSI HBA's
    Multipathing (MPIO)
The use of redundant storage network components responsible for transfer of data between the server and the storage (Cabling, adapters, switches and software)
The partioning of a fabric into smaller subsets to restrict interference, added security and simplify management, it's like VLAN's in networking
See my EMC zoning section for more details


NetApp Terminology

Now that we know how a NetApp is configured from a hardware point of view, we now need to know how to present the storage to the outside world, first some NetApp terminologies explained

A collection of disks that can have either of the below RAID levels, the aggregate can contain up to 1176 disks, you can have many aggregates with the below different RAID levels. An aggregate can contain many volumes (see volumes below).
  • RAID-4
  • RAID-DP (RAID-6) better fault tolerance
One point to remember is that a aggregate can grow but cannot shrink, the disadvantage with RAID 4 is that a bottleneck can happen on the dedicated parity disk, which is normally the first disk to fail due to it being used the most, however the NVRAM helps out by only writing to disks every 10 seconds or when the NVRAM is 50% full.
Raid Group (Pool)
Normally there are three pools 0, 1 and spare
  • 0 = normal pool
  • 1 = mirror pool (if syncMirror is enabled)
spare = spares disks that be used for growth and replacement of failed disks


When a aggregate is mirrored it will have two plexes, when thinking of plexes think of mirroring. A mirrored aggregated can be split into two plexes.

Volume (Flexible)

This is more or like a traditional volume in other LVM's, it is a logical space within an aggregate that will contain the actual data, it can be grown or shrunk as needed


Write anywhere filesystem layout is the filesystem used, it uses inodes just like Unix. Disks are not formatted they are zeroed.
By default WAFL reserves 10% of a disk space (unreclaimable)


The Logical Unit Number is what is present to the host to allow access to the volume.

A frozen read-only image of a volume or aggregate that reflects the state of the new file system at the time the snapshot was created, snapshot features are
  • Up to 255 snapshots per volume
  • can be scheduled
  • Maximum space occupied can be specified (default 20%)
File permissions are handled

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