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RAID Groups |
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RAID Groups |
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RAID Groups
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RAID Groups |
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RAID Groups |
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Users can expand a RAID group, add hard drive(s) to a RAID group, migrate a RAID group, configure a spare drive, enable a bitmap and recover a RAID group for a chosen volume, while the data contained in the RAID group remains intact. In this chapter, the following topics are covered:
RAID group types
Refer to the table below for explanations on RAID types:
Field |
Description |
Single Disk |
A single, stand-alone RAID group can be set up for your NAS. However, this setup does not provide any redundancy protection. So, in the event that a disk is corrupted or otherwise damaged, all data on that disk will be lost. |
RAID 0 Striping |
A striping RAID group combines two or more disks into one large, logical disk. It offers the fastest disk access performance but no data redundancy protection in the event of disk failure or damage. The disk capacity is the sum of all disks. Disk striping is usually used to maximize disk capacity or to accelerate disk access speed. Please note that RAID 0 configuration is not recommended for storing sensitive data. |
RAID 1 Mirroring |
Disk Mirroring protects your data by automatically mirroring the contents of one disk to the second disk in the mirrored pair. It provides protection in the event of a single disk failure. The storage capacity is equal to the capacity of the smallest single disk, as the second disk drive is used to back up the first disk drive. RAID 1 configuration is suitable for storing sensitive data on a corporate or personal level. |
RAID 5 |
RAID 5 configurations are ideal for organizations running databases and other transaction-based applications that require storage efficiency and data protection. A minimum of 3 hard disks are required to create a RAID 5 group. The total capacity of the RAID 5 group is equal to the size of the disk with the smallest capacity in the array times the number of (hard disk – 1). It is recommended (though not required) that only hard drives of the same brand and capacity are used to establish the most efficient hard drive capacity.
In addition, if your system contains four disk drives, it is possible to use three drives to implement a RAID 5 data array with the fourth drive kept as a spare disk. In this configuration, the system will automatically use the spare disk to rebuild the array in the event of a physical disk failure. A RAID 5 configuration can survive one disk failure without losing any system functionality. When a disk fails in RAID 5, the disk volume will operate in the "degraded mode". There is no more data protection at this stage, and all the data will be lost if the unit suffers a second disk failure. A failed disk should be immediately replaced. Users can choose to install a new disk after turning off the server or hot-swap the new disk while the server is running. The status of the disk volume will change to "rebuilding" after installing a new disk. Your disk volume will return to a normal status once the volume rebuilding process is complete.
Note: To install a new disk when the server is running, first ensure the disk volume is in "degraded" mode. Or, wait to hear two long beeps after the disk crashes and then insert the new disk in place of the failed disk. |
RAID 6 |
RAID 6 is ideal for critical data protection needs. To create a RAID 6 group, a minimum of 4 hard disks are required. The total capacity of a RAID 6 group is equal to the size of the disk with the smallest capacity in the array times the number of (hard disks – 2). It is recommended (though not required) to use identical hard drives to establish the most efficient hard drive capacity. RAID 6 can survive 2 disk failures and the system can still operate properly.
Note: To install a new disk when the server is running, first ensure the disk volume is in "degraded" mode. Or, wait to hear two long beeps after the disk crash and then insert the new disk in place of the failed disk. |
RAID 10 |
RAID 10 is a combination of RAID 1 (mirroring) and RAID 0 (striping), without parity. RAID 10 is a stripe across a number of disks to provide fault tolerance and high speed data transfer. The storage capacity of a RAID 10 group is equal to the size of the disk with the smallest capacity in the array times (the number of hard disks in the array/2). It is recommended that only hard disk drives of the same brand and capacity are used to create a RAID 10 group. RAID 10 is suitable for high volume transaction applications, such as a database, that require high performance and fault tolerance. A maximum of 1 failed disk from each disk pair is allowed in RAID 10.
Note: To install a new disk when the server is running, first be sure the disk volume is in the "degraded" mode. Or, wait to hear two long beeps after the disk crashes and then insert the new disk in place of the failed disk. |
JBOD |
Two or more disks can be combined into one larger volume. Files are sequentially saved on physical disks. The overall capacity of the linear disk is the sum of the capacity of all disks. This configuration does not provide disk failure protection; failure of one drive will cause the entire array to be lost. A JBOD group is generally used for storing a large amount of data. It is not appropriate for storing sensitive data. |
Bad Block Management (BBM)
BBM uses the bad block list (log) for each drive and uses it to allow the system to fail single blocks rather than entire drives. This feature is especially useful for RAID arrays and is automatically enabled if your disks support BBM. Bad blocks in different sections on different drives can cause a RAID array to fail. With BBM, the RAID array can be functional even when encountering bad blocks.
Note: BBM support is only available for RAID 5 and RAID 6. |
With this function, RAID group capacity can be expanded by replacing hard disk drives in a RAID group array one by one. This option is supported for the following RAID types: RAID 1, RAID 5, RAID 6 and RAID 10. Follow these steps to expand a RAID group:
| 1. | Go to "Storage Manager" > "STORAGE" > "Storage Space". |
| 2. | Double click a storage pool to bring up the Storage Pool Management page. |
| 3. | Select a RAID group and click "Manage" > "Expand Capacity". |
| 4. | Select at least one hard disk drive. After the description displays "Please remove this drive", remove the hard disk drive from the NAS or expansion enclosure. |
| 5. | After the description displays "You can replace this drive", plug in the new hard disk drive to the drive slot. Repeat the same process for all hard drives to be replaced. Click "Expand Capacity" to continue. |
| 6. | Click "Yes". |
| 7. | The chosen RAID group is expanded. |
With this function, new drive members can be added to a RAID group. This option is supported for RAID 5 and RAID 6 drive configurations.
Follow these steps to add the hard disk drive(s) to a RAID group:
| 1. | Go to "Storage Manager" > "STORAGE" > "Storage Space". |
| 2. | Double click a storage pool to bring up the Storage Pool Management page. |
| 3. | Select a RAID group and click "Manage" > "Add Hard Drive". |
| 4. | Select hard disk drive(s) from the list to add to the chosen RAID group and click "Apply". |
| 5. | Please note that all data on the selected hard drive(s) will be erased. Click "Yes" if you are certain about this. |
| 6. | The chosen hard disk drive(s) are added to the selected RAID group. |
With this function, a RAID configuration can be migrated to a different RAID configuration. This option is supported for the following drive configurations: Migrating single drives to RAID 1; Migrating RAID 1 to RAID 5; Migrating RAID 5 to RAID 6. Follow these steps to migrate a RAID configuration:
| 1. | Go to "Storage Manager" > "STORAGE" > "Storage Space". |
| 2. | Double click a storage pool to bring up the Storage Pool Management page. |
| 3. | Select a RAID group and click "Manage" > "Migrate". |
| 4. | Select the hard disk drive(s) from the list and click "Apply". |
| 5. | Please note that all data on the selected hard disk drive(s) will be erased. Click "Yes" if you are certain about this. |
| 6. | The chosen RAID configuration is migrated to the new one. |
With this function, a spare drive can be added to or removed from a RAID 1, RAID, 5, RAID 6, or RAID 10 configuration. Unlike a global spare drive, the drive in this case will be dedicated to the RAID group. Follow these steps to configure a spare drive:
| 1. | Go to "Storage Manager" > "STORAGE" > "Storage Space". |
| 2. | Double click a storage pool to bring up the Storage Pool Management page. |
| 3. | Select a RAID group and click "Manage" > "Configure Spare Drive". |
| 4. | Select the hard disk drive(s) to be configured as spare drive and click "Apply". |
| 5. | Please note that all data on the selected hard disk drive(s) will be erased. Click "Yes" if you are certain about this. |
| 6. | The chosen disk drives are added as spare drive. |
This function can reduce the rebuild time after a crash, or the time length required to remove/re-add a hard disk. This feature does not improve disk read/write performance and may even cause slight performance degradation. However, if an array has a bitmap, a hard disk can be removed and re-added, and only changes in blocks need to be made since the removal (as recorded in the bitmap) can be re-synced. To enable a bitmap, follow these steps:
| 1. | Go to "Storage Manager" > "STORAGE" > "Storage Space". |
| 2. | Double click a storage pool to bring up the Storage Pool Management page. |
| 3. | Select a RAID group and click "Manage" > "Enable Bitmap" and then "OK". |
To disable a bitmap,
| 1. | Go to "Storage Manager" > "STORAGE" > "Storage Space". |
| 2. | Double click a storage pool to bring up the Storage Pool Management page. |
| 3. | Select a RAID group and click "Manage" > "Disable Bitmap" (only available after a bitmap has been enabled) and then "OK". |
Note: Bitmap support is only available for RAID 1, RAID 5, RAID 6 and RAID 10. |
Recovering Failed RAID Disk Volumes
This can recover failed RAID disk volumes from the "Inactive" status to a normal state (RAID 1, RAID 5, RAID 6 and RAID 10 will be recovered to the degraded mode; RAID 0 and JBOD will be recovered to the normal state.) Before recovering a failed disk volume, please confirm that all hard disks of that disk volume are properly seated in the NAS drive bays. Once recovery is completed, immediately back up your data on the disk(s) in case the disk volume fails again.
Inactive RAID disk volumes can only be recovered if the minimal number of healthy disks required for the RAID configuration is available on the NAS. For example, in a RAID 5 configuration with three disks in the array, at least two healthy hard disk drives are required available in the NAS for volume recovery. If not, this RAID volume cannot be recovered. Refer to the following table for the minimal number of hard disks required to recover a RAID group:
RAID group |
Minimal number of hard disks required for recovery |
RAID 1 |
1 |
RAID 5 |
Number of disks - 1 |
RAID 6 |
Number of disks - 2 |
RAID 10 |
Number of disks / 2; (1 hard drive per RAID 1) |
Follow these steps to recover a failed RAID group:
| 1. | Go to "Storage Manager" > "STORAGE" > "Storage Space". |
| 2. | Double click a storage pool to bring up the Storage Pool Management page. |
| 3. | Select a failed RAID group. |
| 4. | Click "Manage" > "Recover". |
| 5. | The chosen RAID group will be recovered. |
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© 2017 QNAP Systems, Inc. |
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