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Disk Pools

1. Introduction to disk pools

A pool is constructed of disk groups. Disk groups that can be a part of the pool are the following: 

  • Data disk groups - this are the disks that contain the data. Each data disk group may have a number of disks that may fail before loosing data. All disk groups in a pool must have the same allowed number of disks that may fail before loosing data. Choosing data disk groups that will support disk failures will result in lower available space on the group – depending on the number of disks that may fail (eg. if a data disk group of 5 disks may allow two disks to fail before loosing data then the total available space on the disks group will be reduced by 40%). 
  • Spare disk group - this group contains disks that are not actively used but will automatically replace a data disk if it fails. Adding spare disks is optional.
  • Read cache disk group - this group contains disks that are actively used to speed up the data reading process. It is recommended to use high speed disks (SSD) in this group. Adding disks to this group is optional.
  • Write cache disk group - this group contains disks that are actively used  to speed up the data writing process. The same as for read cache disk group it is recommended to use only high speed disks(SSD) in this group. Adding disks to this group is optional.

The recommended number of disks in a data disk group that may allow only one failing disk before loosing data is between 3 and 9. For a large number of disks on the system for better performance try using more groups. For large space requirements you may take into consideration using more disks per group. 

2. Creating disk pools using the web interface on Syneto Storage

The image below illustrates the disk pool section:

 

The available disks for creation are listed in the disks section. Disks used in other disk pools are greyed out and cannot be used in a new disk pool. A new pool can be created by clicking the ‘New disk pool’ button. The image below contains the options available at creation:

To add a disk in a ‘Data Disk Group’, ‘Spare Disk Group’, ‘Read Cache Disk Group’ or ‘Write Cache Disk Group’ you have to drag an available disk to the corresponding group. While dragging, the destination will highlight green if you are allowed to drag the disk there.

Adding multiple data disk groups is done by clicking on the ‘New data disk group’ button.

NOTE: All disks in one disk pool must have identical sizes! After dragging the first disks, only disks of the same size can be added.

If the disks have been used previously in another Syneto Storage disk pool, you will need to force creation.

NOTE: The color beneath each disk number represents the controller. If you have more than four controllers, you may choose to create multiple data disk groups that do not have more than two disks from the same controller. This way you can create a pool that is immune to controller failure in addition to disk failure. 

When you have completed your desired configuration you can finish the creation by clicking the ‘Add’ button or you can cancel the operation by hitting the ‘Cancel’ button on the bottom of the page.

3. Replacing a faulted disk

The true power of pools comes into action when one or more or your disks fail. Considering your diskpool configuration a certain number of disks may fail before data loss.
When replacing a faulted disk make sure that the replacement disk is of the same size as the one faulted. 
To replace the faulted disk take the following steps:

Identify the name and position of the faulted disk – this can be done using the web interface. A faulted disk is marked with an exclamation mark. 

  1. Eject the faulted disk from the bay.
  2. Insert the new disk in its place.
  3. Refresh disks configuration and identify the new disk – using the web interface access the diskpool section and refresh the current disk configuration. Identify the new disk and map it.
  4. Replace the old disk with the new one in pool configuration – connect in console , enter the unsupported shell by executing ‘unsupported shell’. Now to replace the disk execute: zpool replace name_of_disk_pool name_of_faulted_disk name_of_new_disk
  5. Refresh disks configuration using the web interface.

At this point the faulted disk is replaced with the new disk and the system is automatically restoring the data on the new disk.

4. Replacing a faulted disk in rpool’s mirror

All the conditions from 3. apply here. To replace the disk, follow the steps:
  1. Eject the faulted disk from the bay.
  2. Insert the new disk in its place.
  3. Connect in console and enter the unsupported shell by executing “unsupported shell”.
  4. Detach the disk by executing the following command: “zpool detach name_of_rpool name_of_faulted_disk”
  5. Insert the disk in rpool by executing the next command: “rpool-mirror name_of_faulted_disk”
At this point the faulted disk is replaced with the new disk and the system is automatically restoring the data on the new disk.