Data Recovery Glossary

SAS to Synology Hybrid RAID

Data Recovery Glossary home

List of pages

A - Access Rights to ASCII

B - Backup to BTRFS

C - CANON_DC to Cross-linked Files

D - DAS to Dynamic Disk

E - ECC to External Hard Drive

F - Failed Disk to fsck

G - Gigabyte to GUID

H - Hard Drive to Hybrid Disk

I - IDE to Internal Drive

J - JBOD to Jumper

L - LBA to LVM

M - Megabyte to Motherboard

N - NAS to Nuke & Pave

O - Operator Error to Overwritten Data

P - Parallel ATA to PSU

Q - QNAP to Quota

R - RAID to Resident File

S - SAS to Synology Hybrid RAID

T - Tailpacking to TrueCrypt

U - UDMA to USB Thumbdrive

W - WD to Write-Through Cache




SAS (Serial Attached SCSI) - the interface for data exchange between various devices. It uses serial data transfer. SAS is compatible with SATA - it is possible to attach a SATA hard drive to a SAS controller.


SATA (Serial ATA) - the standard on the connector and on the method of data transfer. Usually SATA is used for hard disks and CD drives because for these devices fast data transfer is required. There are three types of SATA - SATA 1 with the maximum transfer speed of 150 Mb/sec, SATA 2 with the maximum speed of 300 Mb/sec, and SATA 3 with the maximum speed of 600 Mb/sec.


SCSI (Small Computer System Interface) - the interface to connect various devices on one bus. Originally, SCSI was used for many types of devices, including scanners and CD drives. Lately, SCSI is mostly used for hard drives.


SD (Secure Digital) - a type of removable flash memory card. SD cards are produced by many memory card manufacturers. By now, the maximum capacity of SD cards is 32 GB. SD cards are usually formatted to FAT32 filesystem.


A hard drive manufacturer known by

  1. the Barracuda family of hard drives,
  2. the Cheetah 15,000 RPM high-performance family of hard drives,
  3. Seagate Momentus XT hybrid hard drive.


Sector - a minimum unit of disk space on a disk.

Secure erase

Secure erase - the process in which the data is deleted irreversibly by overwriting it. Usually data is overwritten a few times with random data.


Slab - a part of the disk with the size of 256 MB. Storage Spaces divides each of disks in a pool into such parts, which eventually form virtual disks.


Slack - a place at the end of a cluster which is not used for the file data. A filesystem always allocates the disk space cluster-by-cluster, however, a file rarely occupies an integral number of clusters. For example, for the file with the size of 2000 bytes the cluster with the size of 4096 bytes is allocated. In this example 2096 bytes at the end of cluster are not used and are called "slack".


S.M.A.R.T. (Self Monitoring And Reporting Technology) - the technology which monitors the state of hard drive and tries to predict a disk failure. For an end-user, S.M.A.R.T.-enabled motherboard sometimes provides an advance warning about imminent disk failure, allowing for a quick backup. However, the predictions are not very reliable.

Spanned volume

Spanned volume, also called JBOD - a set of disks concatenated to a single large storage. The data is written onto a spanned volume by filling the disks one by one. Spanned volume provides neither fault tolerance nor speed increase. However, unlike RAID, several disks with different sizes can be combined into a spanned volume without losing capacity.


SSD (Solid State Drive) - a device to store data which uses flash memory chips, with a size and a type of connection identical to that of hard drive.

Storage Spaces

Storage Spaces - a capability introduced in Windows 8 Server to manage disk space efficiently. The best effectiveness is achieved when Storage Spaces works in conjunction with ReFS filesystem. Storage Spaces has a bulk of different features, thin provisioning being the most known of them.


Striping - the method of writing data to a storage device where data blocks are written to disks in turn. Used in RAID levels 0, 10, 5, and 6.


Superblock - one of the important structures in traditional UNIX filesystems. It is used in many filesystems (ext, UFS, ReiserFS) to keep track of the filesystem. Usually a superblock size is 1024 bytes. The following parameters are typically defined in a superblock:

  • filesystem size;
  • filesystem parameters, such as cluster (block) size;
  • location of control structures of filesystem.

Synology Hybrid RAID

SHR (Synology Hybrid RAID) - is a RAID management technology based on Linux LVM, which is used in Synology NASes, similar to NETGEAR's X-RAID2. With SHR, you can use disks of different sizes in one unit thus maximizing usable storage capacity.

Copyright © 2010 - 2024