Network Attached Storages (NAS) are devices aimed at storing and sharing files over a local network. These storages work as small file servers and don't perform any functions like e-mailing, authentication or file management.
A NAS device consists of a control board which provides network access to data and from one to several disks that can be organized as a RAID system to extend disk storage space, increase operational speed and enhance storage reliability. Most NAS retailers like Iomega, Synology and Buffalo offer software-based RAID as a function of an embedded OS, while others, like Promise, supply hardware-based RAID.
NAS storages work with retailer-specific file systems. The most commonly used are Ext3 and XFS of special Linux editions. At the same time, such retailers as Adaptec offer BSD-based solutions (e.g. SnapOS) and use custom UFS editions. Modern NAS storages can also use various releases of ZFS file system. The type of the file system of NAS storage doesn't influence access to network files and storage operation, but rather data recovery chances in case of storage failures and data loss.
Typical NAS storages can be divided into a few groups according to the complexity.
Primarily, NAS devices serve as shared storages that provide access to data over a local network. Most NASes have common storage structure and data organization. Actual data layout, however, depends on NAS vendor and the embedded configuration.
Each NAS disk arranges data on four disk partitions:
Firmware-reserved partition. This partition contains technical information about firmware. On 1TB TeraStation, for example, this partition is 0.6GB in size identified as “Linux native” and formatted with SGI XFS file system. Available on the 1st and the 2nd NAS disks only.
Swap partition. Contains swap for NAS firmware.
Data partition. This partition stores user data. On 1TB TeraStation, for instance, it is 232GB partition, identified as “Linux native”. Actual size depends on the NAS settings.
Padding partition. This partition is used to unify data partition size regardless of an actual number of disks. The size depends on a disk model. On 1TB TeraStation it is identified as “Linux native”, yet, it has no file system.
Disk partitioning style is standard DOS-style (MBR-based) and is readable by any software.
RAID configuration and data organization
Depending on the configuration, RAID offers several possible data organization methods for Data partitions:
RAID5 - the most widely-used configuration. In RAID5 mode user data are located across the data partitions of all four disks. Usual parity distribution is backward-dynamic (left-symmetric). Stripe size depends on the settings (usually 64KB). Disk order for RAID is consequent: the 1st disk of NAS is the 1st disk of RAID etc. Data partition on TeraStation, for example, is formatted as SGI XFS, on Synology – as Ext3.
RAID0. Usually user data are arranged as a single full-capacity storage or a pair of RAID0 stripe sets with two independent partitions (different “share” virtual folders on NAS). Both contain the same file system type but different data.
RAID10 or RAID0+1. The mirror of two RAID0 stripe sets or a stripe set of two mirrors. User data is arranged in the same way as in RAID0, but only with one “share” and both stripe sets contain the same information.
JBOD. Data partitions are concatenated to yield maximum storage capacity. User data is spanned across all data partitions.
Individual drives. In NAS drives that are not organized in RAID each data partition bases on an independent file system.
Before you start data recovery from your NAS you should identify actual configuration of the storage. For more information about RAID systems, please, refer to RAID: structure and recovery article.
Prepare for recovery
Despite increased reliability of NAS storages, they are still exposed to failures and loss of valuable information. Most typical causes of data loss of NAS storages include system failures, software malfunctions, control board failures or human errors.
When recovery is required?
NAS storages don't provide direct access to their drives, thus data recovery process requires storage disassembling and connecting its drives to a recovery machine. Please read "HOW TO: Connect IDE/SATA drive to a recovery PC" or the detailed instructions. Besides, when you remove NAS drives, it's recommended to mark their order with paper stickers or a soft ink marker in order to re-assemble the storage properly.
Due to their evident advantages NAS storages have already become an essential part of everyday work for home users and SMBs. NAS vendors began to offer quite cost-efficient solutions, which increased their availability on the market. Despite enhanced reliability of these storages, these days they are still exposed to failures resulting in storage inaccessibility or even data loss.
Most common data loss cases include:
- Loss of NAS link;
- Offline array or 'four red lights';
- Data corruption due to power outages;
- Firmware crash or failed boot;
- Disk(s) failure;
- Controller failure;
- Electrical or mechanical damages.
User errors causing data loss include:
- Faulty firmware update and reset of embedded RAID settings;
- File deletion;
- Rebuilding embedded RAID configuration on live data and disks re-formatting.
If you are sure that NAS disks didn't sustain any physical damage and remained workable, you can start data recovery following the instructions given below. If the disks have any physical defects caused by mechanic, thermal or electric damage, it's strongly recommended to have your data examined in a specialized data recovery laboratory.
For efficient recovery from NAS storages SysDev Laboratories offers UFS Explorer software. UFS Explorer RAID Recovery was specially developed to work with complex RAID systems. UFS Explorer Professional Recovery offers professional approach to data recovery process. Other UFS Explorer products work with RAID systems via plug-ins and modules. All the software applies powerful mechanisms to allow you to achieve maximum possible recovery result and are 100% reliable to guarantee complete safety of the data stored on your NAS. For more detailed information, please, go to http://www.ufsexplorer.com/products.php.