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Article reference number: FS-FBS-20110228-I01
Last proofread : 16 August 2011
Version : 1.0


Back-up to network disk (NAS)

This article will present how to use network disks (NAS - Network Attached Storage) to store backup copies. We will tell you which network disk to choose and how to set up LAN to make backup and data recovery efficient and not too heavy on the corporate network.



Network disk as a storage for backup copies

Network disks, due to the multiple purposes they serve, enjoy ever greater popularity. Companies use them not only to provide access to files in LAN but also to store backup copies. One of the major rules of security is to store backup copies at a different location than the backed up data. With network disks, which are usually small and can be managed remotely, it is easy to meet that requirement. A network disk can be left in a locked room which cannot be accessed by unauthorized parties. If we add that virtually all professional network disk models enable data to be saved on several hard disks at a time (RAID), it turns out that this is a very good place for storing backup copies.


Which network disk to choose?

To answer this question, you have to consider in what way the network disk will be used. In the Ferro Backup System it is possible to use network disks to store backups in two ways: as the master backup storage site or as a replication site, that is a site where additional backup copies are stored. Mechanisms such as backup delta or rotation copies (versioning) used in the Ferro Backup System require fast access to master backup storage. Therefore, if we decide to use a network disk as master storage, we need to choose a network disk meeting the best random access efficiency parameters. Because network disks nevertheless provide lower efficiency than local hard disks and the possibility of I/O errors due to connection failure is much higher, it is best to use network disks as an additional backup storage, namely to replicate backups. A network disk used only as extra security may have a slower data read and write speed as it will only be used in the event of a breakdown of the master backup storage site.

Another parameter that should be taken into account when choosing a network disk intended for backup storage is the type of network transmission protocols supported by this device. The way data can be sent to the NAS server helps to quickly distinguish network disks intended for home purposes from professional solutions. Details of network protocols used for file transfer are described later in the article. Here it is worth mentioning that network disks with an implemented iSCSI protocol will be the best choice. If the network disk is intended only as additional security (backup replica storage), alternatively one can choose a device with no implemented iSCSI protocol which supports data transmission through the CIFS protocol.


Connecting network disk to backup server

Backup of data including large files or entire hard disks entails a high network load even despite using solutions such as compression at the remote computer's end or differential copies and delta copies, built into the Ferro Backup System. When using the network disk as the master backup storage site, the LAN load will be even greater as, apart from the backup itself, the backup server must also use the network connection to read and write backups. In cases where the network disk is used as emergency backup storage, this problem will no longer be so important (replication can be scheduled to run at night), but it is still worth adopting the solutions mentioned below.

Backup server - network disk connection

Backup server - network disk connection should best be ensured by a dedicated LAN section


To minimize the corporate LAN load during backup to the network disk, it is best to separate the backup server - network disk connection from other network segments. The connection may be separated by properly setting up the router to filter out network traffic between the NAS disk and the backup server from other transmissions. Another, better solution is to use two network cards in the backup server, one of which is connected to the corporate LAN and the other directly to the network disk. In that case, network traffic between the backup server and the network disk will not adversely affect the LAN bandwidth in the company.


Backup copy transmission to network disk

There are many network protocols intended for data transmission. In network disks, protocols most commonly used for writing and reading files are: FTP, CIFS/SMB, iSCSI.

FTP is perfect for sending large files but its efficiency drops drastically if we must send many small files. From the backup system perspective, the greatest disadvantage of this protocol is no random access to files. FTP supports only sequential file read or write - from beginning to end. If we want to read data located in the middle of the file, we need to read the whole file from the beginning. It is also impossible for FTP to modify a file part. We can only delete the old file and save the updated information again or add new data at the end of the file. Due to those constraints, FTP can only be used to replicate backups. Using the network disk as the master backup storage site through FTP is impossible in practice (FTPUSE can emulate direct access to files through FTP, but this solution is not efficient).

CIFS/SMB is very useful for sending both large and small files. In Windows, access to the server using this protocol is provided by the network redirector. Access to the network disk is possible using UNC paths or using a local disk letter to a mapped network share. SMB provides fast random access to files and may be used by the backup server both to run backup storage and as a master backup storage site. The greatest disadvantage of this solution may be problems with reaccessing the file after a temporary loss of network connection. In that case, Windows may return a data write or read error, which may cause backup or data recovery to be interrupted. If we decide, however, to use SMB to run the master backup storage site, we need to ensure maximum network connection stability between the backup server and the network disk.

iSCSI is very often used for SAN mass storage solutions ( Storage Area Network), but it also works very well with NAS disks. Once the operating system and network disk are properly set up, you can use network disk resources (target) as a standard hard disk. Random file read and write is equally fast or even faster than in CIFS/SMB. Moreover, iSCSI implementation in Windows is much more reliable if the network connection is reset than in CIFS/SMB. These properties make iSCSI ideal for writing and reading backups from the replication site and master backup storage.


Summary

Network disks may be used in professional backup systems, but one needs to remember to choose the proper hardware and to ensure a proper network set-up. If a network disk is used as storage for additional backup copies, one can use less efficient network disks which support at least CIFS. For network disks used as the master backup storage, one should use the fastest possible device which supports iSCSI. The backup server should be best connected to the network disk by an isolated LAN fragment.


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