A Pool in Rockstor is a set of disk drives combined and represented as a single volume. Pools have attributes such as redundancy profile and compression to safeguard and store data efficiently. Pools can be expanded or shrunk by adding or removing disk drives. In other words, a Pool is a single or multi device BTRFS filesystem.
Pool related operations can be managed from the Pools screen listed under the Storage tab of the Web-UI.
Creating a Pool¶
Only whole disk drives can be used to create Pools. But they don’t have to be of the same size, which is a great feature of BTRFS. Disks that are partitioned with other filesystems including BTRFS won’t be touched. Whole disks with BTRFS created outside of Rockstor or from a previous install, can however be imported. For more information, see Data Import.
Click on Create Pool button and submit the create pool form to create a pool. There is a tooltip for each input field to help you choose appropriate parameters. Here’s a video showing this operation.
All standard BTRFS redundancy profiles are available when creating a pool.
- Single: This profile offers no redundancy, and is the only valid option for creating a Pool with a single disk drive. It is also recommended if you have multiple disks of different sizes, yielding higher total capacity compared to Raid0. Data is neither mirrored nor striped, so if a disk fails, the entire data of the Pool will be lost.
- Raid0: Two or more disks can be used with this profile when there is no need for redundancy. Both metadata and data are striped across the disks. It is recommended for same size disks. If you have different size disks and no need for redundancy, Single profile provides higher capacity. If a disk fails, the entire data of the Pool will be lost.
- Raid1: Two or more disks can be used with this profile. And both metadata and data are replicated on 2 devices. So a Pool with this profile can sustain a single disk failure.
- Raid5: Two or more disks can be used with this profile, which supports striping + parity. Like Raid1, this profile can sustain a single disk failure. The BTRFS community consensus is that Raid5 support is not yet fully stable and so is *not recommended for production use*.
- Raid6: Three or more disks can be used with this profile, which supports striping + dual-parity. Because of dual-parity, a Raid6 Pool can sustain up to two disk failures at the same time. The BTRFS community consensus is that Raid6 support is not yet fully stable and so is *not recommended for production use*.
- Raid10: This is a Raid0 of Raid1 mirrors, with a minimum requirement of four disk drives. It offers most redundancy at the cost of capacity where a Pool can sustain multiple disk failures at the same time as long as the failed disks are part of different Raid1 groups.
Please see the btrfs wiki for up to date information on all btrfs matters.
Compression can optionally be chosen during Pool creation or it can be set on a previously created Pool. In the latter scenario, compression is applied only to data written after it’s set.
Compression can also be set at the Share level. If you don’t want to enable compression for all Shares under a Pool, don’t enable it at the Pool level. Instead, selectively enable it on Shares.
Besides not enabling compression at all, there are two additional choices
These are optional and meant for more advanced users to provide BTRFS specific mount options. Since a Pool is a filesystem, it is mounted with default options which can be altered by providing one or more of the following. You can find out more about each option from the btrfs wiki mount options section.
A really cool feature in Pool management(powered by BTRFS) is the ability to add or remove disks and change redundancy profile online without access disruption. You can resize a Pool easily from the Web-UI for one of the following reasons
- To change it’s redundancy profile. For example, to go from a RAID10 to RAID1. See Redundancy profile changes.
- To add more disks and increase it’s capacity. See Adding Disks.
- To remove disks and decrease capacity. Removed disks can be reused for other Pools. See Removing Disks.
Pool resize is an online operation that does not cause access disruption. However, depending on size of the Pool, it could take a long time to finish.
Redundancy profile changes¶
You can change Redundancy profiles online with very few restrictions. This video shows how to change a Pool from RAID1 to RAID10.
Disks can be added to a Pool online and expand capacity. This video shows how to expand a RAID1 Pool by adding three disks.
Disks can be removed from a Pool online similar to adding Disks. However, since it results in reduced capacity, this operation can succeed only if the resulting capacity after removal is greater than the current usage. This video shows how to remove two disks from a RAID1 Pool made up of four disks.
A Pool can be deleted as long as it is empty, i.e., there are no Shares remaining in it. So, if you need to delete a Pool, first delete every Share in it. Then, click on the corresponding trash icon for it in the Pools screen under the Storage tab of the Web-UI.
A Pool can also be deleted using the Delete button inside it’s detail screen.
Scrubbing a Pool¶
The scrub operation initiates a BTRFS scrub process in the background. It reads all data from all disks of the Pool, verifies checksums and fixes corruptions if detected and possible. To find out more, see the btrfs wiki scrub section.
To start a scrub, go to the Pool’s detail page and click on the Start a new scrub button in the Scrubs tab. The button will be disabled during the scrub process and enabled again once the scrub finishes. The progress of a running scrub operation is displayed in a table. Refresh the page to update the information.
A periodic scrub is a proactive strategy to fix errors before too many accumulate. You can schedule it using the Scheduled Tasks screen under System tab of the Web-UI.
Balance a pool¶
The balance operation initiates a BTRFS balance process in the background. It spreads data more evenly across multiple disks of the Pool. It is automatically triggered after a Pool resizing operation, which is the main purpose of this feature. A standalone balance operation is intended for advanced users who can judge for themselves if it is necessary. To find out more, see the btrfs wiki balance section.
To start a balance, go to the Pool’s detail page and click on the Start a new balance button in the Balances tab.