Adding disks

About adding disks

When you add disks to a filer, you need to insert them in a disk shelf according to the disk shelf manufacturer's instructions. They then become hot spare disks. You also add the disks to a volume with the vol add command.

You can use disks of various sizes in a volume according to the following rules:

If an added disk replaces a failed data disk, its capacity is limited to that of the failed disk.
If an added disk is not replacing a failed data disk and it is not larger than the parity disk, its full capacity (subject to rounding) is available as a data disk.

When to add disks

You add disks when

You want to add storage capacity to the filer
You are running out of hot spare disks

Considerations when adding disks to the filer

Original disk configuration

Network Appliance recommends adding RAID groups and/or disks before the file system is 80% to 90% full.

The number of disks and RAID groups at initial filer configuration affects read and write performance. A greater number of disks means a greater number of independently seeking disk-drive heads reading data. Write performance can also benefit from more disks; however, the difference can be masked by the effect of NVRAM and the manner in which WAFL manages write operations.

Adding more disks to the filer

Network Appliance recommends adding disks in multiples of 8 to 14 for overall improved performance. However, as more disks are configured, the performance increase levels off. Performance is affected more with the fewer disks you add until the striping across all the disks levels out. When the striping levels out, there is an increase in operations per second and a reduced response time.

The ideal time to add more disks to meet future storage requirements is before the applied load places stress on the existing array of disks, even though adding more disks at this time will not significantly improve the filer's current performance.

Adding hot spare disks to the filer

You should periodically check the number of hot spares you have on your filer and add disks if you have fewer than one per shelf. If there are no hot spare disks, you should add disks to disk shelves so they become available as hot spares.

For more information, see Hot spare disks.

Ascertaining the number of hot spare disks

To ascertain how many hot spare disks you have on your filer, complete the following step.

Step	Action
1	Enter the following command: vol status -s Result If there are hot spare disks, a display like the following appears, with a line for each spare disk, grouped by checksum type: Spare disks for block or zoned checksum volumes RAID Disk HA.ID HA SHELF BAY CHAN Used (MB/blks) Phys(MB/blks) --------- ----- ------------ ---- -------------- -------------- spare 7.17 7 2 1 FC:A 0 17046/34910224 spare 7.26 7 3 2 FC:A 0 34209/70061520 ... Spare disks for zoned checksum volumes only RAID Disk HA.ID HA SHELF BAY CHAN Used (MB/blks) Phys(MB/blks) --------- ----- ------------ ---- -------------- -------------- spare 7.21 7 2 5 FC:A 0 17366/35566480 spare 7.19 7 2 3 FC:A 0 17366/35566480

Step

Action

Enter the following command:

vol status -s

Result

If there are hot spare disks, a display like the following appears, with a line for each spare disk, grouped by checksum type:

Spare disks for block or zoned checksum volumes

RAID Disk   HA.ID    HA SHELF BAY    CHAN    Used (MB/blks)   Phys(MB/blks)

---------   -----    ------------    ----    --------------   --------------

spare       7.17     7    2    1     FC:A    0                 17046/34910224

spare       7.26     7    3    2     FC:A    0                 34209/70061520

...

Spare disks for zoned checksum volumes only

RAID Disk   HA.ID    HA SHELF BAY    CHAN    Used (MB/blks)   Phys(MB/blks)

---------   -----    ------------    ----    --------------   --------------

spare       7.21     7    2    5     FC:A    0                 17366/35566480

spare       7.19     7    2    3     FC:A    0                 17366/35566480

Rules for adding disks to a volume

You add disks to a volume according to the following rules:

You can add only hot spare disks to a volume.
You must specify the volume to which you are adding the disks.
You can add block checksum disks to zoned checksum volumes; you can add only block checksum disks to block checksum volumes.
The disks must come from the same spare disk pool (if you are using mirrored volumes).

Parity disk determination

If an added disk is larger than an existing parity disk, the added disk replaces the smaller disk as the parity disk, and the smaller disk becomes a data disk. This enforces a Data ONTAP rule that the parity disk must be at least as large as the largest data disk in a RAID group.

Note
In volumes configured with RAID DP (which uses RAID groups that contain both a regular parity disk and a double, or dParity, disk) the larger added disk replaces any smaller regular parity disk, but its capacity will be downsized, if necessary, to avoid exceeding the capacity of any smaller-sized the dParity disk.

Adding new disks to the filer

To add new disks to the filer, complete the following steps.

Note
In the following procedure, the NearStore R100 appliance and the original-capacity R150 appliance use disks on SCSI-attached shelves. The R150 appliance with upgraded 24 TB capacity and the R200 appliance use disks on Fibre-Channel-attached shelves.

Step	Action
1	If the disks are...	Then...
	Fibre Channel disks or on Fibre-Channel-attached shelves	Go to Step 2.
	SCSI disks or on SCSI-attached shelves	Enter the following command, and go to Step 2: disk swap
2	Install one or more disks according to the hardware guide for your disk shelf. Note On FAS270 and FAS270c appliances, a disk ownership assignment might need to be carried out. See Disk ownership assignment on an FAS270/FAS270c appliance. Result The system displays a message confirming that one or more disks were installed and then waits 15 seconds as the disks are recognized. The system recognizes the disks as hot spare disks. Note If you add multiple disks, the system might require 25 to 40 seconds to bring the disks up to speed as it checks the device addresses on each adapter.
3	Verify that the disks were added by entering the following command: vol status -s Result The number of hot spare disks in the RAID Disk column under Spare Disks increases by the number of disks you installed.

Adding new disks to a volume

To add new disks to a volume, complete the following steps.

Step	Action
1	Verify that hot spare disks are available for you to add by entering the following command: vol status -s
2	Add the disks to a volume by entering the following command: *vol add vol-name* ndisks[@disk-size] \| -d disk-name...** vol-name is the name of the volume to which you are adding the disks. ndisks is the number of disks to use. disk-size is the disk size, in gigabytes, to use. You must have at least ndisks available disks of the size you specify. disk-name is the disk ID of one or more spare disks; use a space to separate disk IDs. The disk ID is under the HA.ID column in the `vol status -s` display. Note If you want to use block checksum disks in a zoned checksum volume and there are still zoned checksum hot spare disks, use the `-d` option to select the disks. Examples The following command adds four 36-GB disks to the thisvol volume: vol add thisvol 4@36 The following command adds the disks 7.17 and 7.26 to the thisvol volume: vol add thisvol -d 7.17 7.26

Step

Action

Verify that hot spare disks are available for you to add by entering the following command:

vol status -s

Add the disks to a volume by entering the following command:

vol add vol-name ndisks[@disk-size] | -d disk-name...

vol-name is the name of the volume to which you are adding the disks.

ndisks is the number of disks to use.

disk-size is the disk size, in gigabytes, to use. You must have at least ndisks available disks of the size you specify.

disk-name is the disk ID of one or more spare disks; use a space to separate disk IDs. The disk ID is under the HA.ID column in the vol status -s display.

Note
If you want to use block checksum disks in a zoned checksum volume and there are still zoned checksum hot spare disks, use the -d option to select the disks.

Examples

The following command adds four 36-GB disks to the thisvol volume:

vol add thisvol 4@36

The following command adds the disks 7.17 and 7.26 to the thisvol volume:

vol add thisvol -d 7.17 7.26

Note
When adding disks to a volume, Data ONTAP attempts to distribute I/O loads, such as alternating host adapters, to improve reconstruction performance. You can override this behavior by specifying the disks you want.

Adding new disks to a RAID group

If a volume has more than one RAID group, you can specify the RAID group to which you are adding disks. To add new disks to a specific RAID group of a volume, complete the following step.

Step	Action
1	Enter the following command: vol add vol-name ndisks[@disk-size] \| -d disk-name... -g raidgroup raidgroup is a RAID group in the volume specified by vol-name. Example The following command adds two disks to RAID group 0 of the vol0 volume: vol add vol0 -g rg0 2

Note
The number of disks you can add to a specific RAID group is limited by the raidsize setting of the volume to which that group belongs. See Chapter 4, RAID Group Management for more information.

Forcibly adding disks to volumes

The following are situations that would fail if you tried to add disks to a volume:

The disks specified in the vol add command would cause the disks on an unmirrored volume to span adapters.
The disks specified in the vol add command add disks to a RAID group other than the last RAID group, thereby making it impossible for the file system to revert to a version prior to Data ONTAP 6.4.

To force Data ONTAP to add disks in these situations, complete the following step.

Step	Action
1	Enter the following command: vol add vol-name -f [-g `raidgroup`] -d disk-name... Note You must use the `-g` raidgroup option to specify a RAID group other than the last RAID group in the volume.