Fedora Linux

6.2.3.1. ...booting from a RAID array?

During the early stages of the boot process, no RAID driver is available. However, in a RAID 1 (mirroring) array, each element contains a full and complete copy of the data in the array and can be used as though it were a simple volume. Therefore, only RAID 1 can be used for the /boot filesystem.

The GRUB boot record should be written to each drive that contains the /boot filesystem (see Lab 10.5, 'Configuring the GRUB Bootloader')

6.2.3.2. ...mixing and matching USB flash drives, USB hard disks, SATA, SCSI, and IDE/ATA drives?

RAID can combine drives of different types into an array. This can be very useful at times; for example, you can use a USB hard disk to replace a failed SATA drive in a pinch.

6.2.3.3. ...mirroring to a remote drive as part of a disaster-recovery plan?

Daily disk or tape backups can be up to 24 hours out of date, which can hamper recovery when your main server is subject to a catastrophic disaster such as fire, circuit-frying power-supply-unit failure, or theft. Up-to- the-minute data backup for rapid disaster recovery requires the use of a remote storage mirror.

iSCSI ( SCSI over TCP/IP) is a storage area network technology that is an economical alternative to fiber channel and other traditional SAN technologies. Since it is based on TCP/IP, it is easy to route over long distances, making it ideal for remote mirroring.

Fedora Core includes an iSCSI initiator , the software necessary to remotely access a drive using the iSCSI protocol. The package name is iscsi-initiator-utils . Obviously, you'll need a remote iSCSI drive in order to do remote mirroring, and you'll need to know the portal IP address or hostname on the remote drive.

Create the file /etc/initiatorname.iscsi , containing one line:

InitiatorName=iqn. 2006-04.com.fedorabook:bluesky

This configures an iSCSI Qualified Name (IQN) that is globally unique. The IQN consists of the letters iqn , a period, the year and month in which your domain was registered ( 2006-04 ), a period, your domain name with the elements reversed, a colon, and a string that you make up (which must be unique within your domain).

Once the initiator name has been set up, start the iscsi server daemon:

# service iscsi start

You may see some error messages the first time you start the iscsi daemon; these can be safely ignored.

Next, use the iscsiadm command to discover the volumes (targets) available on the remote system:

# iscsiadm -m discovery -tst -p 172.16.97.2
[f68ace] 172.16.97.2:3260,1 iqn.2006-04.com.fedorabook:remote1-volume1

If the remote drive requires a user ID and password for connection, edit /etc/iscsid.conf. 

The options indicate discovery mode, sendtargets ( st ) discovery type, and the portal address or hostname. The result that is printed shows the IQN of the remote target, including a node record ID at the start of the line ( f68ace ). The discovered target information is stored in a database for future reference, and the node record ID is the key to accessing this information.

To connect to the remote system, use iscsiadm to log in:

# iscsiadm -m node --record f68ace --login

The details of the connection are recorded in /var/log/messages :

Mar 30 22:05:18 blacktop kernel: scsi1 : iSCSI Initiator over TCP/IP, v.0.3
Mar 30 22:05:19 blacktop kernel: Vendor: IET Model: VIRTUAL-DISK Rev: 0
Mar 30 22:05:19 blacktop kernel: Type: Direct-Access ANSI SCSI revision: 04
Mar 30 22:05:19 blacktop kernel: SCSI device sda: 262144 512-byte hdwr sectors (134 MB)
Mar 30 22:05:19 blacktop kernel: sda: Write Protect is off
Mar 30 22:05:19 blacktop kernel: SCSI device sda: drive cache: write back
Mar 30 22:05:19 blacktop kernel: SCSI device sda: 262144 512-byte hdwr sectors (134 MB)
Mar 30 22:05:19 blacktop kernel: sda: Write Protect is off
Mar 30 22:05:19 blacktop kernel: SCSI device sda: drive cache: write back
Mar 30 22:05:19 blacktop kernel: sda: sda1
Mar 30 22:05:19 blacktop kernel: sd 14:0:0:0: Attached scsi disk sda
Mar 30 22:05:19 blacktop kernel: sd 14:0:0:0: Attached scsi generic sg0 type 0
Mar 30 22:05:19 blacktop iscsid: picking unique OUI for the same target node name iqn.2006- 04.com.fedorabook:remote1-volume1
Mar 30 22:05:20 blacktop iscsid: connection1:0 is operational now

This shows that the new device is accessible as /dev/sda and has one partition ( /dev/sda1 ).

You can now create a local LV that is the same size as the remote drive:

# lvcreate main --name database --size 128M
Logical volume 'database' created

And then you can make a RAID mirror incorporating the local LV and the remote drive:

# mdadm --create -l raid1 -n 2 /dev/md0 /dev/main/database /dev/sdi1

mdadm: array /dev/md0 started.

Next, you can create a filesystem on the RAID array and mount it:

# mkfs -t ext3 /dev/md0
mke2fs 1.38 (30-Jun-2005)
Filesystem label=
OS type: Linux