User's Manual

Solution The maximum number of virtual disks that can be added to a cache is 64. If you try to add the

65th virtual disk, the add operation fails.

Disabling Cache Fails

Probable Cause

• The Fluid Cache disk is in use or mounted.

• The Fluid Cache disk contains dirty data that cannot be flushed to disk.

Solution

• For the Fluid Cache disk is in use or mounted issue, you cannot disable caching on a

Fluid Cache disk unless it is first unmounted. To unmount the disk, run the command:

fldc --disable --disk= <disk_name>--umount. The disk is now

disabled and unmounted.

• For the Fluid Cache disk contains dirty data that cannot be flushed to disk issue, you

cannot disable caching on a Fluid Cache disk if it is in a failed state. Resolve any back

end storage issue causing the back end PERC virtual disk to fail and reactivate the disk

before you reattempt to disable it. To disable caching, run the command: fldc --

disable --disk= <disk_name>--umount

. If reactivation fails, you can

restore from a backup. If a backup is restored, you do not need the data in cache. You

can use the disable command and add the --discard flag to destroy all the dirty blocks

in cache.

CAUTION: Do not use the --discard option unless you know that the removal of

dirty data in cache does not cause any data integrity issues. Use of --discard

renders your data unrecoverable.

NOTE: It may take some time for the disable command to complete.

Fluid Cache I/O Errors

Probable Cause The I/O caching errors occur when Fluid Cache for DAS cannot read or write from a back end

virtual disk that the PERC card controls.

Solution If the Fluid Cache layer does not exist, the PERC card sends I/O errors to applications when a

back end virtual disk fails. Since the Fluid Cache for DAS exists, it intercepts I/O errors from the

PERC card and passes them through to any application reading or writing to the back end

virtual disk which the PERC card has identified as missing. For a list of issues that can cause

I/O errors, see the topic “Fluid Cache Disk Status Has Failed” in this section. Some of the

issues that can generate I/O errors include the following:

• A back end PERC virtual disk has failed.

• A data volume is no longer available.

• Multiple PCIe SSDs have failed simultaneously.

Use Dell OpenManage to identify the reason for the I/O error. Use the PERC card controls to

identify the physical device that has failed.

Operating System Fails

If your operating system fails, it may be possible for you to recover your Fluid Cache for DAS

configuration.