FreeNAS FAQ
Welcome to the FreeNAS FAQ
In this area of our site, you will find the answers to the frequently asked questions, as well as answers to How do I and Did you know questions. Please feel free to post a comment on any Q&A.
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| Category | Q&A | Last Q&A published |
 General
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5 | What is ZFS? |
Last published Q&A
Here is a list of the last Q&As that were published.
ZFS is a file system designed by Sun Microsystems for the Solaris Operating System. ZFS is open-source software and has therefore also been ported to FreeBSD the OS behind FreeNAS.
A traditional file systems resides on single hard drive and if you want to use more than one hard drive they need to be combined either with RAID or with a volume manager.
ZFS is different, all ZFS filesystems are built on top of virtual storage pools called zpools. A zpool is constructed of virtual devices, which are themselves constructed of physical hard drives (or indeed files or hard drive partitions).
Hard drives within a virtual device may be configured in different ways, depending on needs and space available: non-redundantly (similar to RAID 0), as a mirror (RAID 1) of two or more devices, as a RAID-Z group of three or more devices (which is similar to RAID 5), or as a RAID-Z2 group of four or more devices (which is similar to RAID 6).
You can find more technical details on ZFS at Wikipedia.
A traditional file systems resides on single hard drive and if you want to use more than one hard drive they need to be combined either with RAID or with a volume manager.
ZFS is different, all ZFS filesystems are built on top of virtual storage pools called zpools. A zpool is constructed of virtual devices, which are themselves constructed of physical hard drives (or indeed files or hard drive partitions).
Hard drives within a virtual device may be configured in different ways, depending on needs and space available: non-redundantly (similar to RAID 0), as a mirror (RAID 1) of two or more devices, as a RAID-Z group of three or more devices (which is similar to RAID 5), or as a RAID-Z2 group of four or more devices (which is similar to RAID 6).
You can find more technical details on ZFS at Wikipedia.
iSCSI (Internet SCSI) is an evolution of the SCSI protocol, which allows SCSI commands to be sent over a network. It allows two hosts to negotiate and then exchange SCSI commands using IP networks. The result is that a remote device with iSCSI capabilities can be seen to be a local disk drive but the commands and data for that device are being sent over the network rather than down a cable in the machine.
In iSCSI clients (called initiators) are able to send SCSI commands to SCSI storage devices (targets) on remote servers.
FreeNAS can act as an iSCSI initiator or and iSCSI target.
In iSCSI clients (called initiators) are able to send SCSI commands to SCSI storage devices (targets) on remote servers.
FreeNAS can act as an iSCSI initiator or and iSCSI target.
RAID
Redundant Array of Inexpensive Disks or Redundant Array of Independent Disks (as it is more commonly called now) is a technology that uses two or more hard disk drives to achieve greater levels of performance and reliability.
A RAID distributes data across several physical disks which look to the operating system and the user like a single disk. Several different arrangements are possible (called RAID levels). Usually all the disks are of the same capacity.
RAID Levels
RAID levels 0, 1, and 5 are the most commonly found, and cover most requirements.
RAID 0 (striped disks) distributes data across several disks in a way which gives improved speed and full capacity, but all data on all disks will be lost if any one disk fails.
RAID 1 (mirrored disks) uses two (possibly more) disks which each store the same data, so that data is not lost so long as one disk survives. Total capacity of the array is just the capacity of a single disk. The failure of one drive, in the event of a hardware or software malfunction, does not increase the chance of a failure or decrease the reliability of the remaining drives (second, third, etc).
RAID 5 (striped disks with parity) combines three or more disks in a way that protects data against loss of any one disk; the storage capacity of the array is reduced by one disk. The less common RAID 6 can recover from the loss of two disks.
Redundant Array of Inexpensive Disks or Redundant Array of Independent Disks (as it is more commonly called now) is a technology that uses two or more hard disk drives to achieve greater levels of performance and reliability.
A RAID distributes data across several physical disks which look to the operating system and the user like a single disk. Several different arrangements are possible (called RAID levels). Usually all the disks are of the same capacity.
RAID Levels
RAID levels 0, 1, and 5 are the most commonly found, and cover most requirements.
RAID 0 (striped disks) distributes data across several disks in a way which gives improved speed and full capacity, but all data on all disks will be lost if any one disk fails.
RAID 1 (mirrored disks) uses two (possibly more) disks which each store the same data, so that data is not lost so long as one disk survives. Total capacity of the array is just the capacity of a single disk. The failure of one drive, in the event of a hardware or software malfunction, does not increase the chance of a failure or decrease the reliability of the remaining drives (second, third, etc).
RAID 5 (striped disks with parity) combines three or more disks in a way that protects data against loss of any one disk; the storage capacity of the array is reduced by one disk. The less common RAID 6 can recover from the loss of two disks.
Network Attached Storage
In the mid 1980's two computer companies independently started to work on ways to access files, over the network. These two companies were Sun Microsystems and Microsoft. The Sun Microsystems method, which was for their UNIX operating system, is known as the Network File System (NFS) and was subsequently implemented in almost all versions of the Unix operating system including Linux. The Microsoft solution (which they actually joint developed with IBM in the initial stages) became known as SMB (Server Message Block) but in later years was renamed as the Common Internet File System (CIFS). The general functionality of NFS and CIFS is very similar and with either installed on a networked computer it can read and write to the file system on another computer on the network.
This ability to use a remote computer (a fileserver) to store files led to many companies deploying large centralized NFS Servers or Windows Servers which were accessed by hundreds and maybe thousands of Unix workstations or PC clients. Users would then be encouraged to store all important files on these servers as the IT staff would back up the servers regularly and so back up the important user files.
With modern needs for multimedia storage combined with high speed local networks, a new kind of storage solution has appeared, Network Attached Storage or NAS for short. A NAS server is similar to a traditional file server in many ways, especially in respects to the hardware side of the server. But a NAS server is much more specialized than a traditional office or departmental server in that it only provides access to storage via the network. It is not designed to run other applications such as databases or email servers which other types of server might.
In the mid 1980's two computer companies independently started to work on ways to access files, over the network. These two companies were Sun Microsystems and Microsoft. The Sun Microsystems method, which was for their UNIX operating system, is known as the Network File System (NFS) and was subsequently implemented in almost all versions of the Unix operating system including Linux. The Microsoft solution (which they actually joint developed with IBM in the initial stages) became known as SMB (Server Message Block) but in later years was renamed as the Common Internet File System (CIFS). The general functionality of NFS and CIFS is very similar and with either installed on a networked computer it can read and write to the file system on another computer on the network.
This ability to use a remote computer (a fileserver) to store files led to many companies deploying large centralized NFS Servers or Windows Servers which were accessed by hundreds and maybe thousands of Unix workstations or PC clients. Users would then be encouraged to store all important files on these servers as the IT staff would back up the servers regularly and so back up the important user files.
With modern needs for multimedia storage combined with high speed local networks, a new kind of storage solution has appeared, Network Attached Storage or NAS for short. A NAS server is similar to a traditional file server in many ways, especially in respects to the hardware side of the server. But a NAS server is much more specialized than a traditional office or departmental server in that it only provides access to storage via the network. It is not designed to run other applications such as databases or email servers which other types of server might.
FreeNAS is free piece of software that turns a PC into network attached storage. It supports connections from Microsoft Windows, Apple OS X, Linux and FreeBSD. It supports RAID, has a simple web GUI and modest system requirements.
FreeNAS is an embedded operating system. This means it is compact, efficient and dedicated to just one task, in this case NAS. Once FreeNAS is installed on a PC, the PC becomes a dedicated NAS, it can’t do other general tasks at the same time.
Features
FreeNAS supports the following network access protocols
* CIFS (via Samba)
* FTP
* NFS
* AFP
* RSYNC
* iSCSI
It also features:
* Support for S.M.A.R.T
* Local and Active Directory user authentication
* Software RAID (0,1,5)
The FreeNAS website is: http://www.freenas.org/
FreeNAS is an embedded operating system. This means it is compact, efficient and dedicated to just one task, in this case NAS. Once FreeNAS is installed on a PC, the PC becomes a dedicated NAS, it can’t do other general tasks at the same time.
Features
FreeNAS supports the following network access protocols
* CIFS (via Samba)
* FTP
* NFS
* AFP
* RSYNC
* iSCSI
It also features:
* Support for S.M.A.R.T
* Local and Active Directory user authentication
* Software RAID (0,1,5)
The FreeNAS website is: http://www.freenas.org/