Using the Cache Group Node

> Using the Cache Group Node

> On Windows

> The configuration is complete, and the virtual drives (VDs) configured are now ready to be cached by the Nytro XD solution. The newly configured Cache Group node appears on the MegaRAID Storage Manager GUI.

> Use the configured Nytro XD solution device node by using the MegaRAID Storage Manager application or StorCLI or MegaCLI utility.

> On Linux

> The Nytro XD solution creates the device mapper device nodes with the same names as the underlying VD names, but with an additional nytroxd- prefix. This device node is placed under the /dev/mapper directory. This is true for all of the partitions that exist on the VD configured in the Nytro XD solution.

> NOTE When a VD is successfully added to the Nytro XD solution, it automatically runs kpartx/partprobe to create these nodes.

> For example: If you issue the following command to configure a VD:

> # MegaCli64 XD -AddVd 0x5000c5000f8f8c1f
> Device "0x5000c5000f8f8c1f" added successfully.
> Exit Code: 0x00

> Corresponding to the VD /dev/disk/by-id/scsi-35000c5000f8f8c1f, the Nytro XD solution creates a node /dev/mapper/nytroxd-scsi-35000c5000f8f8c1f that represents the cached VD. This node must be used by applications for caching to take effect for this VD.

> # MegaCli64 XD -VdList

> Vendor: SEAGATE

> Model: ST9146703SS

> Device Node: /dev/disk/by-id/scsi-35000c5000f8f8c1f [/dev/sdm]

> SCSI ID: 0x5000c5000f8f8c1f

> Capacity: 136.732 GB

> Device state: Online

> Mapped Path: /dev/mapper/nytroxd-scsi-35000c5000f8f8c1f

> Exit Code: 0x00

> If /etc/fstab contains the following entry:

> /dev/disk/by-id/scsi-35000c5000f8f8c1f /data ext4 defaults 1 2

> It must be changed to the following entry:

> /dev/mapper/nytroxd-scsi-35000c500f8f8c1f /data ext4 defaults 1 2

> NOTE Do not use /dev/disk/by-id/scsi-35000c5000f8f8c1f after you configure this VD in the Nytro XD solution; this might cause data corruption

> CAUTION When the Nytro XD solution creates a device mapper device node for a VD (for example, /dev/mapper/nytroxd-scsi-35000c5001d70ae43), the same VD is also available for direct access (through /dev/disk/by-id/scsi-35000c5001d70ae43, which usually is a symbolic link to the underlying sd device under /dev, for example, /dev/sdg). Even when a cache device (Nytro WarpDrive card) is configured under Nytro XD solution, the device node for that (for example, /dev/sdb) is also available for direct access. Exercise caution and make sure that you do not inadvertently directly access or update these disks outside of the Nytro XD solution control. Such an access is illegal, and any updates made through the direct access can lead to data corruption on these disks. Be aware that this is a feature/limitation of the Linux device model.

DB15-000917-02-January 2013
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