Supported storage technologies

eCryptfs is a filesystem-level encryption solution natively supported by the Linux kernel starting from version 2.6.19. Layered on top of the primary filesystem, eCryptfs protects the content of its files and directories, making them accessible only when mounted with the correct passphrase. File names can be secured as well when the corresponding option is enabled during the setup. The default cipher of eCryptfs is AES, but it can also employ others algorithms via a manual configuration (BlowFish, DES3, CAST5, CAST6, TwoFish etc.). All the cryptographic metadata is stored in the header of the encrypted file, which provides high flexibility of handling files while preserving their confidentiality.

VeraCrypt is an open-source encryption tool available for the Windows, macOS, and Linux platforms. The software allows protecting sensitive data by moving it into a secured file container (a virtual disk represented by an encrypted file in the system). The container itself has a pre-defined size and can also be made hidden. All files that are saved to it get encrypted on-the-fly. Their decryption is possible only when the container is mounted with the correct password. A mounted container can be accessed in the OS like a regular volume. As an alternative, VeraCrypt can be used to encrypt entire system drives, external storage devices or specific partitions. Among the utilized ciphers are AES, Serpent, Twofish, Camellia, and Kuznyechik. Additional protection can also be achieved by using a key file or PIM along with the password.

VeraCrypt is based on TrueCrypt, another open-source encryption utility that has been widely applied until 2014 but is no longer maintained due to certain safety concerns. Though VeraCrypt is capable of opening and converting TrueCrypt volumes, the two formats are not compatible.

BitLocker is Microsoft’s proprietary full-disk encryption feature available in certain editions of Windows starting from Windows Vista as well as in Windows Server 2008 and later. Providing encryption for entire volumes, BitLocker protects the content of a drive by applying an AES (Advanced Encryption Standard) encryption algorithm with a 128-bit or 256-bit key to make it unreadable when the system is offline and prevent unauthorized access. A hardware component BitLocker works in conjunction with is called a Trusted Platform Module (TPM) – a specialized security chip on the motherboard installed in most newer computers which stores the BitLocker recovery key.

Apple’s APFS file system employed in macOS High Sierra and later has native support for encryption, which makes it possible for data to be encrypted directly at the file system level, instead of wrapping a volume in an additional logical layer using CoreStorage and encrypting it at the block level, as has been done in earlier versions of macOS with HFS+. APFS volumes are encrypted with the help of an AES (Advanced Encryption Standard) encryption algorithm in the XTS mode using a 128-bit key.

Data Deduplication is Microsoft’s storage efficiency improvement feature available since Windows Server 2012. Its purpose is to find and remove duplicate data, allowing the user to store more information in less physical space. If enabled, the deduplication mechanism regularly scans the content of a volume in search for repeated chunks of data, placing only one copy to a file in the Chunkstore folder under System Volume Information and updating file metadata with a pointer to that unique copy referred to as a reparse point. This feature is supported by NTFS and ReFS volumes.

Some hardware/operating systems automatically create additional partitions on a disk containing service information. Such partitions are required for the system to work correctly and store no user data. Among them are:

• Swap partition is usually created by Linux and is used to extend RAM for resource-heavy tasks – when memory gets filled up, the storage space from this partition can be allocated to run additional applications.
• GPT partition stores a copy of information related to the way the drive is partitioned, like where partition start/end and which of them are bootable. Such a partition can be found on drives that use the GPT (GUID Partition Table) partitioning system.
• Boot partition is a disk partition which keeps special configuration files with code required to boot the operating system or contains reserved space necessary for system boot.

Core Storage is a format of logical volumes introduced by Apple in macOS 10.7 (Lion) which has been the basis for the FileVault 2 and Fusion Drive technologies up to macOS 10.13 (High Sierra) – in case either of these features is enabled, a Core Storage volume is created by default.

Serving as a layer been the disk partitioning scheme and the HFS+ file system, it basically combines one or several physical volumes (actual storage devices) into a logical volume group, which can contain one or more logical volumes. However, unlike traditional LVMs, Core Storage doesn’t support thin provisioning, dynamic volume expansion or redundancy, and its use is rather limited to the implementation of the full-disk encryption and “hybrid” storage concepts in Mac.

Linux Unified Key Setup or LUKS is a standard used by Linux and other platforms to implement full-disk encryption on various block devices. Relying on the device mapper subsystem and the dm-crypt module of the kernel, LUKS supports a variety of encryption methods, like AES, BlowFish, TwoFish and many others, which can be applied in different chaining modes. The format offers the possibility to create multiple keys for access to the encrypted data and allows manipulating these keys.

LVM stands for Logical Volume Manager and is a Linux storage management technology which provides more administration flexibility in comparison to the traditional method of disk partitioning. Utilizing the device mapper framework, LVM combines existing storage devices into logical groups, which act as pools of storage space used to dynamically allocate logical units as needed. LVM offers a wide variety of advanced features, among which are striping, mirroring, snapshots and Thin Provisioning.

Thin Provisioning serves for cost-efficient allocation of storage space, allowing administrators to assign logical volumes more storage capacity than actually exists in the system. Each thin provisioned logical volume is bound to a storage pool of free space referred to as a thin pool and is given a virtual size which can be as large as the whole pool itself. Unlike standard logical volumes, which reserve storage blocks upon creation, blocks in thin volumes are allocated as they are written.

The HP EVA (Enterprise Virtual Array) is a family of server storage systems released by Hewlett-Packard for mid-range and enterprise customers since 2002. EVA storage units rely on a special technology called Vraid. From 8 to 240 hard drives are combined into a disk group, within which a Vdisk is created and is striped across all the drives in the group. Four levels of redundancy are available for each Vdisk: Vraid 0 (data striping), Vraid 1 (data mirroring), Vraid 5 (data striping with single parity), Vraid 6 (data striping with double parity). A single disk group can be used for multiple Vdisks which may have the same or different Vraid levels.

HP LeftHand (StoreVirtual) is a family of SAN storage solutions for Windows and Linux server virtualization environments provided by Hewlett-Packard. LeftHand storage units make use of a specific storage technology called Network RAID. Network RAID is similar to the traditional RAID but is applied across the network on network attached storage devices, which can be physical or virtual SAN appliances. The technology offers several levels of data protection, which define how many copies of data blocks are written across the network on these devices: NR0 (data striping), NR10 (two-way data mirroring and data striping) NR10+1 (three-way data mirroring and data striping) NR10+2 (four-way data mirroring and data striping). The NR5 and NR6 options are also available (similar to RAID 5 and RAID 6), but they are very rarely used. Multiple volumes with different NetworkRAID levels can co-exist on one LeftHand cluster.

SANsymphony is a software-defined storage platform aimed at enterprise consumers, shipped by DataCore since 2000. This storage virtualization solution allows pooling resources of various storage devices connected via fiber channel, iSCSI or directly and creating virtual volumes from this combined pool. A single virtual volume can include several physical disks or consume a portion of a single disk. Such virtual volumes can be mirrored synchronously or asynchronously to ensure data protection.

Storage Spaces is a storage virtualization feature available in Windows 8/8.1/10 and Windows Server 2012/2012 R2/2016 which provides an easy way to create software-defined storage by grouping a number of physical drives into a single storage pool and use its capacity to create virtual disks called storage spaces. A storage space can be thin or thick, appears to Windows as a regular disk, and can hold one or more logical volumes. One of the four resiliency types are available for each storage space: simple (no resiliency), two-way mirror (two copies of data are written to different drives), three-way mirror (three copies of data are written to different drives), parity (similar to the traditional RAID 5).

Drobo is a series of multi-disk NAS and DAS devices developed by Drobo Inc. since 2007. A Drobo unit can feature from 4 up to 12 drive bays, in which drives of different capacities, types and spindle speeds can be inserted. Drobo DAS is normally recognized by the host PC as an ordinary USB drive and is managed by the file system defined by the host computer. A home-oriented Drobo NAS box applies ext3 and is presented to the operating system as network storage with a single volume, in contrast to professional models, which usually give the possibility to split up the storage into several volumes or Logical Unit Numbers (LUNs).

To combine multiple physical disks into single storage and ensure data safety, Drobo utilizes a proprietary RAID-based technology called BeyondRAID. BeyondRAID employs a combination of RAID 1 and RAID 5 to achieve single redundancy and a combination of parity and diagonal parity for double redundancy, while the protection algorithm is chosen by BeyondRAID itself on the basis of data availability needs at the given moment. RAID sets are not created over the whole disks but over the regions on them of several tens of megabytes, which are then combined in zones, from which the allocation of file system clusters is carried out.

Zettabyte File System or ZFS is a combination of a file system and logical volume manager originally created by Sun Microsystems for Solaris which is now used in Linux and other UNIX-based operating systems, usually for large-scale storage environments. With ZFS, it is possible to pool all available storage devices (local HDDs/SSDs, SANs, shared devices, etc.) which will be managed as a single entity, and expand this pool by adding more disks to a live system for additional capacity. A ZFS volume is simply a ZFS file system created from a ZFS pool. Such volumes can be simple, mirror and RAID-Z. A simple ZFS volume spans across a series of drives in a pool and can be compared to RAID 0 but with file corruption prevention and other benefits of ZFS.

RAID-Z is a fault tolerance option offered by the ZFS file system. A RAID-Z volume is created in a ZFS storage pool consisting of at least three disks. RAID-Z is similar to a software-based RAID 5 and has an analogous data distribution scheme (a stripe set with single distributed parity) but it doesn’t use stripes of a fixed width: each logical block is its own stripe width and is spread across all the devices.

For higher protection, RAID-Z2 and RAID-Z3 are available as well, which allow the system to withstand the failure of two or even three disks.

Btrfs is a modern Linux file system, which, among other features, offers native RAID support, whose management is much more flexible in comparison to traditional Linux mdadm. Btrfs-RAID doesn’t require any preliminary disk size or count calculations: any number of disks of any size can be attached to the array, while the system automatically balances the data across the disks in accordance with the chosen RAID level. The supported RAID levels include RAID 0, RAID 1, RAID 5, RAID 6 and RAID 10.

EqualLogic is a line of iSCSI-based SAN and NAS systems manufactured by Dell for small and medium-sized businesses. Depending on the model, the system may utilize hard disk drives or mix them with SSDs in a single array. Disk arrays, which are referred to as members, may be of different types (RAID 5, RAID 6, RAID 10, RAID 50, RAID 60) and get organized in a group of up to 16. A single member consists of from 16 to 48 drives and can be segmented into pools. Such pools contain volumes which are presented over the network and are used by virtual machine hosts or other computers.

WD My Cloud Home is a line of consumer NAS products designed by Western Digital. The devices are available in both singe-drive (My Cloud Home) and dual-drive options (My Cloud Home Duo). The drives of the latter are combined into a single logical unit using the spanning, striping or mirroring technique. The storage is presented to the end user as a single shared volume accessible over the Internet through a web-based interface or the accompanying applications for PC, Mac, Android or iOS. Though Ext4 is used as the main file system to store user data on WD My Cloud Home units, its implementation in this case differs considerably from the typical Linux variant of the Ext file system. The file names and directories on WD My Cloud Home volumes are defined by the system itself while the ones specified by the user are linked to them using a special database, which also stores the unique ID for each file and other metadata, including the information placing the file in the directory hierarchy. Such a database is essential for transforming the “technical” structure of the storage to its user-comprehensible form.

Intel Optane is a range of storage and memory solutions based on 3D XPoint memory, a type of non-volatile solid-state memory that offers lower latency, faster access and higher endurance compared to traditional NAND flash. Optane products come in several forms, including a small cache drive that accelerates the performance of a slower SATA hard drive (e.g., Intel Optane Memory, Intel Optane Memory M); a hybrid module combining an Optane cache with a larger NAND SSD on the same M.2 card (e.g., Intel Optane H10/H20); an NVMe Optane SSD used as standalone high-speed storage; a persistent memory module that works alongside DRAM as memory extension.

Caching configurations involving Optane, such as Intel Optane Memory, require special handling. When acceleration is enabled, the system presents both drives as a single virtual volume, similar to RAID 0. Intel’s Rapid Storage Technology (RST) driver monitors file access patterns and determines which data should be cached onto the faster Optane drive. Consequently, portions of the operating system and user files may reside only in the Optane cache, without being written to the main HDD or SSD. Meanwhile, critical metadata used to manage the cache is typically stored at the end of the primary drive. In view of this, successful data recovery is not possible without the presence of both storage components and proper reconstruction of the logical volume.

OpenBSD offers software RAID functionality through the kernel softraid subsystem. This subsystem allows users to combine multiple partitions into a single volume that appears as a regular sd device in the OS (the standard SCSI disk interface in OpenBSD).

A softraid volume is a virtual disk composed of multiple chunks, which are portions of storage assigned with the RAID filesystem type, typically partitions on physical drives.

The softraid subsystem supports various RAID configurations called disciplines: RAID 0 (data is striped across all chunks for performance); RAID 1 (data is mirrored on each chunk for redundancy); RAID 1C (similar to RAID 1, but with encryption applied); RAID 5 (data is striped across chunks with floating parity for fault tolerance); CONCAT (chunks are concatenated end-to-end without redundancy); CRYPTO (encryption-only discipline, which can be used alone or combined with other disciplines).

Some Drobo devices have an extra slot underneath called the Drobo Accelerator Bay, designed for an optional mSATA SSD used as a cache. This cache speeds up storage performance by storing frequently used ("hot") data on the SSD module, managed by proprietary Drobo software. The SSD cache does not constitute part of the main BeyondRAID set and usually isn’t involved in Drobo recovery. However, it can hold important information like file system metadata and small user files. To protect this data during power loss, Drobo relies on an internal battery, which allows the device to keep running and flush this data to the primary storage. However, if the SSD cache is suddenly removed, the NAS is powered off improperly or its hardware fails, some data may not be transferred to the main BeyondRAID volume and remain only in the cache. In this case, the volume may lose its integrity unless the cached data is extracted and properly applied.

Some Synology NAS models support SSD caching, which can be configured as either a read-only or write cache. Both cache types use one or more installed SSDs to improve storage performance by accelerating access to frequently used data (read cache) or by speeding up write operations (write cache).

While the read cache stores only copies of existing data, the write cache holds newly written data before it is committed to the primary drives. This cache may contain critical file system metadata and recently saved files that have not yet been flushed to the main SHR or RAID volume. To safeguard this data in the event of a power outage, Synology devices often include built-in power loss protection.

Despite these measures, if the cache device is unexpectedly removed, the NAS is improperly shut down or a hardware failure occurs, some data may remain only in the write cache. Without this data, the primary array may become inconsistent, making successful data recovery impossible unless the cached content is properly restored and applied.

Some QNAP NAS devices support performance optimization through SSD caching, available in both read-only and write cache modes. When configured for write caching, the system uses one or more SSDs as a temporary storage for incoming data before it is written to the main storage array. This configuration may significantly improve write speeds, especially under high I/O workloads.

Unlike the read cache, which stores copies of frequently accessed data and poses no risk to data integrity, the write cache temporarily holds original data, such as file system metadata and newly written user content that has not yet been committed to the storage pool. Although QNAP provides some power failure protection strategies, they may not always guarantee that this "buffered" data will safely reach the permanent storage.

If the NAS is powered off improperly or the cache SSD is removed before its contents are fully flushed, some critical data may exist only in the write cache. Loss of this data can result in storage inconsistencies and incomplete data recovery. In such cases, it may be necessary to retrieve and reintegrate the cached content.