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These articles provide basic information and helpful recommendations concerning data access and recovery.

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How to choose an optimal operating system for NAS data recovery

Serving the major function of a network device for storing and sharing files NAS storage doesn't require a fully-featured operating system. Normally, the operating system is embedded by NAS vendor. The vendors offer a variety of operating systems for modern NAS devices in most cases principally based on Linux or BSD operating systems.

The basics of NAS architecture

Like any computing device, NAS is composed of the hardware and the software elements. The hardware part includes a processor, RAM and one or more hard disk or solid-state drives housed in an enclosure which is plugged into a router with the help of an Ethernet cable. The software part is represented by the operating system which manages network connection and provides access to data via network file sharing protocols. Such an OS is much more lightweight and less resource-intensive than an ordinary multi-purpose operating system.

As a general rule, NAS manufacturers offer out-of-box solutions with an embedded customized operating system. The majority of them are based on Linux and utilize the Ext4, XFS or Btrfs file system. Yet, some users prefer building their own NAS with the help of open-source NAS operating systems based on BSD.

NAS appliances comprising more than one member disks arrange them into a single logical unit with Linux MD RAID or some vendor-specific RAID implementation, like Drobo BeyondRAID and Synology Hybrid RAID.

The specifics of NAS recovery

Given the above-mentioned peculiarities, a typical NAS box is not capable of running full-featured data recovery software nor can it be connected directly to the PC via USB. In order to read out its data, one needs to open the device and extract its drives as described in the instruction on the removal of NAS disks. After that, they can be connected to a computer as shown in the video guide for connecting SATA disks and processed with data recovery utility.

For multi-drive NAS units, data recovery software with RAID functionality is required, such as UFS Explorer RAID Recovery. This software requires minimum user's efforts while supporting both automatic RAID reconstruction and its manual definition. Yet, some particular technologies employed in certain NAS models, like ones of Drobo, can be handled only by the Professional edition of UFS Explorer.

Note: Data recovery from some NAS models, like LinkStation and TeraStation of Buffalo, MyCloud of Western Digital, DiskStation and RackStation of Synology, TS and TVS series of QNAP, can be performed without disk removal using specialized Network Storage Recovery software. In this case, the device itself must be bootable as the utility connects to the NAS software component and receives information from it over LAN.

Which host OS should I use to recover data?

As a cross-platform software solution, UFS Explorer can be installed on any of the most popular desktop operating systems: Windows, macOS and Linux. Theoretically, each of them is suited to play the role of a host OS during NAS recovery, however, when choosing one you should be aware of the associated difficulties and possible dangers along with ways to overcome them.

Linux

As mentioned above, most NAS vendors integrate custom versions of Linux into their NAS solutions. As a rule, desktop versions of Linux support the same types of file systems and RAID metadata used in Linux-based NAS systems. That being so, it seems quite logical to pick a compatible host OS for NAS recovery: Linux will recognize RAID metadata, build (load) RAID, mount the file system and let you immediately access the data from your NAS. Yet, in view of this compatibility, Linux is able to perform writing operations to the NAS file system that may cause permanent data loss. For this reason, you should be careful and mount the file system in a read-only mode instead of a read-write one.

On the other hand, some NAS retailers extend their file systems with the aim to increase operational speed of the NAS device. A desktop Linux distro may not support such extensions and report file system errors even in the read-only mode. If you run the 'fsck' tool or mount the file system in a read-write mode, this can permanently destroy your data.

Still another danger your files may face is an update of RAID metadata caused by the desktop Linux distro. The Linux OS kernel and the version of software RAID may differ. If Linux updates RAID metadata, the metadata of a new format may fail to be recognized by the NAS. This may result in the auto-repair of NAS which leads to the destruction of the current RAID and creation a new empty storage with the default settings.

In the light of the considerations above, if you are going to use Linux as a host OS anyway, the safest option is to work with disk images instead of the original disks.

macOS

Modern Mac operating systems are unable to read or write to most NAS file systems, yet, they are likely to recognize RAID structures created by the NAS. The main disadvantage of using macOS for NAS recovery is that, if it detects and recognizes RAID structures, it can update them to the latest version or "supported configuration". For example, RAID 10 can be reset to a simple pair of RAID 0 with the loss of all information about mirroring. Consequently, for data recovery from multi-disk NAS units under macOS it is preferable to use disk images to avoid metadata overwriting.

Windows

The operating systems of the Windows family do not recognize NAS file systems and its RAID metadata, eliminating the possibility of implicit damage to the source data. Working with NAS from Windows you may cause damage to your data only by an incorrect action such as data modification with special tools, initialization or formatting of the NAS drives.

If you are unsure concerning the steps you should take in the process of data recovery from your NAS, use Windows as the most reliable host OS that will protect your data from unexpected actions of the operating system. Yet, some Windows drivers offered by third-party retailers for Linux file systems may cause damage or modifications to the file system of your NAS. For this reason, it's strongly recommended disabling all the drivers which can conduct read-write operations on Linux file systems before starting the process of data recovery.

Data recovery procedure

Having prepared the NAS disks for data recovery and decided on the optimal host operating system, one can get on with the process itself. The whole procedure is explained step by step in the NAS recovery manual and demonstrated in the NAS recovery video guide. Useful recommendations as to determining the correct order of NAS drives in an XFS-based device can also be found in XFS NAS: find drives order.

After data recovery

Having completed data recovery, you may continue using your NAS. For this you should put the drives back into your NAS preserving their initial order and then reboot the device. Breaking the correct disk order will lead to the failure of the normal boot process.

Last update: December 19, 2019

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