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On the appliance, storage is divided into arrays, each of which consists of one or more physical hard drives. When defining an array you can choose from the following array types. Each provides a different method of data distribution, resulting in various degrees of storage reliability and array capacity.
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Array Type |
Description |
Linear Concatenation (JBOD) |
In JBOD (“Just a Bunch Of Disks”), disks are simply concatenated, so that they act as one large virtual disk. For example, if you have one 500 GB disk and one 250 GB disk in such an array would act as a 750 GB disk. JBOD provides no data redundancy. If any of the drives in the array fails, the array becomes unreadable. The advantage of JBOD is that you can mix disks of different sizes, without losing capacity. |
RAID0 (Striped) |
In RAID0, data is distributed across multiple disks, in a method called striping. Data is written in small, set amounts to each disk in turn, thus increasing speed with no loss of capacity. Like JBOD, RAID0 provides no redundancy. If one disk fails, the partial data on the other disks will become useless. The size of the array is be the size of the smallest disk in the array, times the amount of drives in the array. RAID0 requires a minimum of two hard drives. |
RAID1 (Mirrored) |
In RAID1, data is duplicated across all disks in the array, so that there is full redundancy. If a disk fails, the array's performance will be reduced (the array will be marked as “Degraded”), but data will not be lost, so long as there is at least one good disk. Data will only be lost if all the disks in the array fail. Since the exact same data must be written on each disk in the array, the array's capacity is limited to that of the smallest disk. RAID1 requires a minimum of two hard drives. |
RAID5 (Striping with distributed parity) |
RAID5 requires three or more disks, and combines striping with distributed parity to protect against data loss. If a disk fails, the array's performance will be reduced (the array will be marked as “Degraded”), but data will not be lost. If two disks fail, data will be lost. The array capacity is: Where RAID5 requires a minimum of three hard drives. |
RAID6 (Striping with dual distributed parity) |
RAID6 is similar to RAID5; however, it uses dual parity to enable the array to survive two disk failures, without data loss. Array capacity is: Where RAID6 requires a minimum of four hard drives. |
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You can also define a standalone drive, which is a single drive with one volume defined on it. To create a standalone drive, format the drive using the Storage Setup Wizard (see Setting Up Storage Using the Storage Setup Wizard). Then create a volume, and in the Specify Volume Details dialog box's Storage Device field, select the drive (see Adding and Editing Logical Volumes). |
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RAID1, 5, and 6 support hot swapping, in which drives are replaced without turning off the appliance. The array remains accessible throughout the hot swap procedure. For further information, see Hot Swapping a Disk in a RAID1, 5, or 6 Array. |
Each array is divided into volumes, which are logical partitions on the array.
The appliance supports the following types of volumes:
A NAS volume is a volume that is formatted with a file system. The appliance acts as a files server for NAS volumes, and the files on such volumes can be accessed using any of the appliance-supported file sharing protocols.
The appliance enables you to take snapshots of NAS volumes. For more information, see Working with Snapshots.
A SAN volume (also called "Raw") is an unformatted volume. The appliance cannot read files on SAN volumes, and therefore file sharing, synchronization, and cloud backup cannot be used with such volumes. In order to access a SAN volume, an iSCSI target should be defined for this volume. The SAN volume will then appear as if it were a physical disk on your PC or server and can be formatted remotely.
