Replacing All Ddms At The Same Time - IBM System Storage DCS3700 Installation, User's, And Maintenance Manual

v Replacing the DDMs one at a time
In this method, you manually fail each DDM, replace it, and wait for the system to restore data to the
new DDM before installing the next DDM. After you install the new DDMs, you can configure them to
make the additional DDM space available. See the procedure in "Replacing the drives one at a time"
on page 107.
Using this method, you can replace the DDMs while the DCS3700 storage subsystem is running,
eliminating the down time that is required if you replace all of them at once. However, this method is
more risky because you can lose data if the drive restoration or storage subsystem reconfiguration
process fails. In addition, the reconstruction process might take a long time. This method works only
on redundant logical drives (RAID 1, 3, 5, or 6). You cannot use this method with any drives
containing RAID 0 logical drives.
Consider backing up your data if you use this method. This safeguards your data if the restoration and
reconfiguration process fails or the new DDM malfunctions.
The method you use depends on the following considerations:
v Which method most closely matches the recommended drive upgrade procedure that is provided in
the operating system or the storage-management software documentation.
v Which RAID level is used on the affected drives. (RAID 0 requires you to replace all the drives at the
same time.)
v How much downtime is acceptable as you swap the DDMs.
v The number of DDMs in an array. Replacing DDMs one at a time is better suited for arrays consisting
of 3 to 5 DDMs. If you have more than 10 DDMs, consider replacing all of them at the same time.
v How much risk of losing data is acceptable. Because the array will be in a degraded state during the
RAID array reconstruction and copyback process as result of replacing an DDM in the array, any new
DDM failure will cause the array to fail (causing a loss of data availability and even a loss of data).
The duration of the reconstruction and copyback process can be quite long, depending on the size of
the RAID array.
v How extensive are the changes to the data while the array is in a degraded state during the RAID
array reconstruction and copyback process as result of replacing an DDM in the array. The more
extensive the data changes, the more work that will need to be performed to restore the data in the
event that the array failed because of an additional DDM failed while the array is in degraded state.

Replacing all DDMs at the same time

Use this procedure to replace all DDMs at the same time. You must use this method if you are upgrading
DDMs containing RAID 0 logical drives. All the data currently on the DDMs is lost when you replace
them; therefore, you must back up all data that is currently on the DDMs. This procedure also requires
you to turn off the DCS3700 storage subsystem, which makes the storage subsystem inaccessible to other
users.
To replace all the DDMs at the same time, perform the following steps:
1. Read the following information:
v The information in "Replacing multiple DDMs" on page 104, particularly the paragraphs that
discuss the differences between the two possible upgrade procedures
v The information in your software documentation regarding DDM upgrades and installation
v The documentation that comes with the new DDMs
Read all precautionary notes, kit instructions, and other information. Kit instructions often contain
the most current information regarding the DDMs and their installation, plus upgrade or servicing
procedures. Compare the kit instructions with this procedure to determine if you need to modify
this procedure.
2. Use the DS Storage Manager software to check the status of the DCS3700. Correct any problems that
are reported.
3. Perform a complete backup of the DDMs that you are replacing.
Chapter 5. Replacing components
105