SoftRAID 3 Manual Excerpts:
Mirror Essentials
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Making Changes to Mirror Volumes
SoftRAID allows you to make changes to your Mirror volumes either to change your configurations or to mitigate state changes, such as failed secondary disks. This section describes the commands under the Volume menu which are used to change Mirror volumes.
Rebuild - Rebuilding a Mirror volume copies all of the data from the Primary disk to any out-of-sync or failed secondary disks. Rebuilding will occur automatically in an out-of-sync situation if the Driver preference “Automatically Start Mirror Rebuilds” has been selected. The Mirror volume is available while the rebuild is in progress. To stop a rebuild, select the Volume tile and select Cancel (command-period) in the Utilities Menu.
Set Primary Disk - The Primary disk designation, originally selected the volume is created, can be changed to another disk using this menu command. Highlight the volume tile and select the command and a window will show the choices for the new Primary.
Split Mirror - Splitting a Mirror allows you to change your Mirror volume configuration either to remove failing disks or to optimize your back-up strategies. Splitting off more than one disk at a time allows you to create new, identical Mirror volumes. Splitting off single disks allows you to create a non-RAID volume or a Read-only secondary volume.
To Split a Mirror:
- Choose the disk(s) - Select the secondary disks you wish to split off.
- Choose the volume type:
non-RAID - This allows you to take a copy of the Primary volume off of the Mirror to another machine and use it.
The SoftRAID application must be installed on the new machine. Other disks can be added to it with the Convert to Mirror command.
Mirror- This allows you to split off a Mirror volume to take to another Mac which has the SoftRAID application
installed. Read-only secondary - A Read-only secondary volume is used for archival purposes and to ensure that
an accurate write-protected copy of data is available. It can only be mounted on a computer which has the SoftRAID driver installed.
Read only secondary volumes are a safe way to split off a secondary from a Mirror and keep it intact until it is added back to the
original Mirror volume with the Convert Read-only secondary command. Some Mirror volume scenarios may involve removing a Primary disk
for copying or changing offsite. In this case, it is important that the secondary disk not be mounted while the Primary is gone. If the disk
is mounted, the SoftRAID driver will change it to a Primary disk since it will detect that the Primary disk is missing. A read-only secondary
volume prevents this from happening.
- Choose the name - The name of the original volume appears in this box. Changing the name of the new volume can help avoid confusion.
- Click on Create - If you have selected a new Mirror, the Primary Disk window will appear asking you to confirm your selection.
The Volume tiles in the Application window will change to show the new split off volume.
Note: If the original volume has been reduced down to just the Primary disk, the state of the volume will be changed to Mirror • no secondary disk unless a Read-only secondary volume was split off in which case it will say Mirror • missing secondary.
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Recover Failed Mirror - A Mirror volume is considered failed if all of its disks received i/o errors. This is a serious condition and may indicate a hardware failure, such as a bad cable or SCSI-PCI card. This command can be used to troubleshoot the situation by rebuilding the failed Mirror. If the cause of the failure is hardware related, then the errors will occur again after the recovery. Malfunctioning hardware should be replaced before creating new Mirror volumes. If the cause of the failure is a crash or brownout, the errors will not recur after the recovery. Recovering a failed Mirror with this command is no guarantee of data integrity.
Add Secondary disk - If you wish to increase the number of disks in a Mirror volume, you can highlight the Mirror volume you wish to add to and choose this menu item. A list of all available disks will appear and you can select the additional secondary disk(s). A Rebuild procedure will be initiated immediately. The volume will show that it is out-of-sync and is being rebuilt until the process is complete.
Remove Missing Secondary Disks - A Mirror volume tile may show a state of missing secondary disk if 1) any secondary disks for that Mirror volume have been disconnected or malfunctioned, or 2) a Read-only secondary volume has been split off using the Split Mirror command. If you wish to continue using the Mirror volume without the missing secondary disks, they can be removed and no longer associate with the volume. Highlight the volume with the missing secondary disk and select Remove Missing Secondary Disks from the Volume menu. An alert will appear asking you to confirm the operation.
If a disk has been removed as a secondary and is mounted at a later date, it will have its status changed to a Primary and its Volume tile will indicate that it is missing a secondary disk.
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Convert Read-Only Secondary Volume - A read-only secondary volume can be added back to its original Mirror volume, or it can be converted to a new non-RAID or Mirror volume. Highlight the volume and select this item. The window will display the conversion options.
Add to original Mirror volume is the the only way a Read-only secondary can be reintegrated with its original Primary disk.
Convert to normal Mirror volume will result in a volume which has no secondary disks. The Add Secondary command described above can be used to make a complete Mirror volume.
Convert to a non-RAID volume removes the read-only designation and the connection to the original Mirror volume.
Convert to Mirror - A non-RAID volume can be converted to a Mirror volume by highlighting the volume and selecting this item. A window will list all available disks which can then be added as secondary disks. Once the secondary disks are selected, the non-RAID volume will be unmounted and changed to be the Primary of the Mirror volume. The volume will be added to the Volume column and a Mirror rebuild operation will start automatically.
The Speed of the Read
SoftRAID mirrors have the ability to perform reads from all disks. This operation is called which is called a stripe read. This results in a Mirror volume with identical read performance as a Stripe volume with the same number of disks. Stripe reads are enabled by default in the SoftRAID preferences. This option is located by selecting the "Driver" tab and finding the option "Use all disks for mirror reads”.
Note: If very different speeds of disks are used, read performance of the Mirror volume will be reduced by the presence of slower disks. In this case it would be best to deselect this option allowing the driver to read just from the Primary disk.
Volume States and Stripe Reads
If a Mirror volume was performing stripe reads and one of the secondary disks received an i/o error, SoftRAID will change the Disk tile to say i/o errors and failed secondary disk. If there are at least two “in-sync” disks available, SoftRAID will continue to perform stripe reads using the remaining disks and the Volume tile will change to i/o errors out-of-sync. The SoftRAID driver will only use the Primary and the in-sync secondary disks for Stripe reads.
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