IBM DS3500 Installation, User & Maintenance Manual page 129

2. Use Table 15 on page 142 to make sure that you replace the hard disk drives
into the correct bays.
Attention: After you remove a drive, wait 70 seconds to allow the drive to spin
down before you replace or reseat the drive. Failure to do so might cause
unpredictable results.
There are two methods for upgrading drives:
v Replacing all the drives at the same time
This method requires that you back up the data on the affected drives and then
turn off the DS3500 storage subsystem.
Attention: Turn off the DS3500 storage subsystem before you turn off the
attached expansion enclosures.
After you replace all the drives, you must reconfigure the new drives and restore
data from backup. See the procedure in "Replacing all drives at the same time"
on page 110.
This is the safest way to exchange drives without losing data. However, this
method might take a long time to complete because of the backup,
reconfiguration, and restoration processes. In addition, other users are not able
to use the storage subsystem (or any expansion enclosures attached to the
storage subsystem) until you finish the procedure. You must use this method on
RAID 0 logical drives.
v Replacing the drives one at a time
In this method, you manually fail each drive, replace it, and wait for the system to
restore data to the new drive before you install the next drive. After you install the
new drives, you can configure them to make the additional drive space available.
See the procedure in "Replacing the drives one at a time" on page 112.
Using this method, you can replace the drives while the expansion enclosures
and the DS3500 are running, eliminating the downtime that is required if you
replace all the drives 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 that contains 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 drive malfunctions.
The method that 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 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 drives.
v The number of drives in an array. Replacing drives one at a time is better suited
to arrays that consist of three to five drives. If you have more than 10 drives,
consider replacing all drives at the same time.
v How much risk of losing data is acceptable. Because the array is in a degraded
state during the RAID array reconstruction and copyback process as result of
replacing a drive in the array, any new drive failure will cause the array to fail
Chapter 5. Replacing components
109