5.7.4. Adding/Removing Storage
Because the need for additional disk space is never-ending, a system administrator often needs to add disk space, while sometimes also removing older, smaller drives. This section provides an overview of the basic process of adding and removing storage.
Note
On many operating systems, mass storage devices are named according to their physical connection to the system. Therefore, adding or removing mass storage devices can result in unexpected changes to device names. When adding or removing storage, always make sure you review (and update, if necessary) all device name references used by your operating system.
5.7.4.1. Adding Storage
The process of adding storage to a computer system is relatively straightforward. Here are the basic steps:
- Installing the hardware
- Partitioning
- Formatting the partition(s)
- Updating system configuration
- Modifying backup schedule
The following sections look at each step in more detail.
5.7.4.1.1. Installing the Hardware
Before anything else can be done, the new disk drive has to be in place and accessible. While there are many different hardware configurations possible, the following sections go through the two most common situations -- adding an ATA or SCSI disk drive. Even with other configurations, the basic steps outlined here still apply.
Note
No matter what storage hardware you use, you should always consider the load a new disk drive adds to your computer's I/O subsystem. In general, you should try to spread the disk I/O load over all available channels/buses. From a performance standpoint, this is far better than putting all disk drives on one channel and leaving another one empty and idle.
5.7.4.1.1.1. Adding ATA Disk Drives
ATA disk drives are mostly used in desktop and lower-end server systems. Nearly all systems in these classes have built-in ATA controllers with multiple ATA channels -- normally two or four.
Each channel can support two devices -- one master, and one slave. The two devices are connected to the channel with a single cable. Therefore, the first step is to see which channels have available space for an additional disk drive. One of three situations is possible:
- There is a channel with only one disk drive connected to it
- There is a channel with no disk drive connected to it
- There is no space available
The first situation is usually the easiest, as it is very likely that the cable already in place has an unused connector into which the new disk drive can be plugged. However, if the cable in place only has two connectors (one for the channel and one for the already-installed disk drive), then it is necessary to replace the existing cable with a three-connector model.
Before installing the new disk drive, make sure that the two disk drives sharing the channel are appropriately configured (one as master and one as slave).
The second situation is a bit more difficult, if only for the reason that a cable must be procured so that it can connect a disk drive to the channel. The new disk drive may be configured as master or slave (although traditionally the first disk drive on a channel is normally configured as master).
In the third situation, there is no space left for an additional disk drive. You must then make a decision. Do you:
- Acquire an ATA controller card, and install it
- Replace one of the installed disk drives with the newer, larger one
Adding a controller card entails checking hardware compatibility, physical capacity, and software compatibility. Basically, the card must be compatible with your computer's bus slots, there must be an open slot for it, and it must be supported by your operating system. Replacing an installed disk drive presents a unique problem: what to do with the data on the disk? There are a few possible approaches:
- Write the data to a backup device and restore it after installing the new disk drive
- Use your network to copy the data to another system with sufficient free space, restoring the data after installing the new disk drive
- Use the space physically occupied by a third disk drive by:
- Temporarily removing the third disk drive
- Temporarily installing the new disk drive in its place
- Copying the data to the new disk drive
- Removing the old disk drive
- Replacing it with the new disk drive
- Reinstalling the temporarily-removed third disk drive
- Temporarily install the original disk drive and the new disk drive in another computer, copy the data to the new disk drive, and then install the new disk drive in the original computer
As you can see, sometimes a bit of effort must be expended to get the data (and the new hardware) where it needs to go.
5.7.4.1.1.2. Adding SCSI Disk Drives
SCSI disk drives normally are used in higher-end workstations and server systems. Unlike ATA-based systems, SCSI systems may or may not have built-in SCSI controllers; some do, while others use a separate SCSI controller card.
The capabilities of SCSI controllers (whether built-in or not) also vary widely. It may supply a narrow or wide SCSI bus. The bus speed may be normal, fast, ultra, utra2, or ultra160.
If these terms are unfamiliar to you (they were discussed briefly in Section 5.3.2.2, “SCSI”), you must determine the capabilities of your hardware configuration and select an appropriate new disk drive. The best resource for this information would be the documentation for your system and/or SCSI adapter.
You must then determine how many SCSI buses are available on your system, and which ones have available space for a new disk drive. The number of devices supported by a SCSI bus varies according to the bus width:
- Narrow (8-bit) SCSI bus -- 7 devices (plus controller)
- Wide (16-bit) SCSI bus -- 15 devices (plus controller)
The first step is to see which buses have available space for an additional disk drive. One of three situations is possible:
- There is a bus with less than the maximum number of disk drives connected to it
- There is a bus with no disk drives connected to it
- There is no space available on any bus
The first situation is usually the easiest, as it is likely that the cable in place has an unused connector into which the new disk drive can be plugged. However, if the cable in place does not have an unused connector, it is necessary to replace the existing cable with one that has at least one more connector.
The second situation is a bit more difficult, if only for the reason that a cable must be procured so that it can connect a disk drive to the bus.
If there is no space left for an additional disk drive, you must make a decision. Do you:
- Acquire and install a SCSI controller card
- Replace one of the installed disk drives with the new, larger one
Adding a controller card entails checking hardware compatibility, physical capacity, and software compatibility. Basically, the card must be compatible with your computer's bus slots, there must be an open slot for it, and it must be supported by your operating system.
Replacing an installed disk drive presents a unique problem: what to do with the data on the disk? There are a few possible approaches:
- Write the data to a backup device, and restore it after installing the new disk drive
- Use your network to copy the data to another system with sufficient free space, and restore after installing the new disk drive
- Use the space physically occupied by a third disk drive by:
- Temporarily removing the third disk drive
- Temporarily installing the new disk drive in its place
- Copying the data to the new disk drive
- Removing the old disk drive
- Replacing it with the new disk drive
- Reinstalling the temporarily-removed third disk drive
- Temporarily install the original disk drive and the new disk drive in another computer, copy the data to the new disk drive, and then install the new disk drive in the original computer
Once you have an available connector in which to plug the new disk drive, you must make sure that the drive's SCSI ID is set appropriately. To do this, you must know what all of the other devices on the bus (including the controller) are using for their SCSI IDs. The easiest way to do this is to access the SCSI controller's BIOS. This is normally done by pressing a specific key sequence during the system's power-up sequence. You can then view the SCSI controller's configuration, along with the devices attached to all of its buses.
Next, you must consider proper bus termination. When adding a new disk drive, the rule is actually quite straightforward -- if the new disk drive is the last (or only) device on the bus, it must have termination enabled. Otherwise, termination must be disabled.
At this point, you can move on to the next step in the process -- partitioning your new disk drive.
5.7.4.1.2. Partitioning
Once the disk drive has been installed, it is time to create one or more partitions to make the space available to your operating system. Although the tools vary depending on the operating system, the basic steps are the same:
- Select the new disk drive
- View the disk drive's current partition table, to ensure that the disk drive to be partitioned is, in fact, the correct one
- Delete any unwanted partitions that may already be present on the new disk drive
- Create the new partition(s), being sure to specify the desired size and partition type
- Save your changes and exit the partitioning program
Warning
When partitioning a new disk drive, it is vital that you are sure the disk drive you are about to partition is the correct one. Otherwise, you may inadvertently partition a disk drive that is already in use, resulting in lost data.
Also make sure you have decided on the best partition size. Always give this matter serious thought, because changing it later is much more difficult than taking a bit of time now to think things through.
5.7.4.1.3. Formatting the Partition(s)
At this point, the new disk drive has one or more partitions that have been created. However, before the space contained within those partitions can be used, the partitions must first be formatted. By formatting, you are selecting a specific file system to be used within each partition. As such, this is a pivotal time in the life of this disk drive; the choices you make now cannot be changed later without going through a great deal of work.
The actual process of formatting is done by running a utility program; the steps involved in this vary according to the operating system. Once formatting is complete, the disk drive is now properly configured for use.
Before continuing, it is always best to double-check your work by accessing the partition(s) and making sure everything is in order.
5.7.4.1.4. Updating System Configuration
If your operating system requires any configuration changes to use the new storage you have added, now is the time to make the necessary changes.
At this point you can be relatively confident that the operating system is configured properly to automatically make the new storage accessible every time the system boots (although if you can afford a quick reboot, it would not hurt to do so -- just to be sure).
The next section explores one of the most commonly-forgotten steps in the process of adding new storage.
5.7.4.1.5. Modifying the Backup Schedule
Assuming that the new storage is being used to hold data worthy of being preserved, this is the time to make the necessary changes to your backup procedures and ensure that the new storage will, in fact, be backed up. The exact nature of what you must do to make this happen depends on the way that backups are performed on your system. However, here are some points to keep in mind while making the necessary changes:
- Consider what the optimal backup frequency should be
- Determine what backup style would be most appropriate (full backups only, full with incrementals, full with differentials, etc.)
- Consider the impact of the additional storage on your backup media usage, particularly as it starts to fill up
- Judge whether the additional backup could cause the backups to take too long and start using time outside of your alloted backup window
- Make sure that these changes are communicated to the people that need to know (other system administrators, operations personnel, etc.)
Once all this is done, your new storage is ready for use.
