The target implementation used earlier can be used only on block devices at the present. This means that we can create block devices and use those, allowing us to use Linux RAID, LVM, Vinum, EVMS or any other volume manager in order to create more efficient storage solutions. In the following procedure we'll use the Linux RAID tools to create a 4 disk RAID0 (striped) volume and then make it avalible as an iSCSI target.
I am personally not a fan of the Linux RAID tools. I use them here simply because it's quick and easy, and so that this procedure is about iSCSI and not an LVM or EVMS tutorial. I highly suggest that if you plan to seriuosly use volumes for iSCSI that you consider using LVM, Vinum, or EVMS.
Procedure 4. Setting up RAID Targets
Ensure that Linux RAID (and LVM if you want it) are compiled into your kernel, and that the mkraid tool is installed.
Create a raidtab for your volume, such as the following.
[root@nexus /etc]# cat raidtab
raiddev /dev/md0
raid-level 0
nr-raid-disks 4
persistent-superblock 1
chunk-size 8
device /dev/sdd1
raid-disk 0
device /dev/sde1
raid-disk 1
device /dev/sdf1
raid-disk 2
device /dev/sdg1
raid-disk 3
[root@nexus /etc]#
Create the volume.
[root@nexus /etc]# mkraid /dev/md0 handling MD device /dev/md0 analyzing super-block disk 0: /dev/sdd1, 17782768kB, raid superblock at 17782656kB disk 1: /dev/sde1, 17782768kB, raid superblock at 17782656kB disk 2: /dev/sdf1, 17782768kB, raid superblock at 17782656kB disk 3: /dev/sdg1, 17782768kB, raid superblock at 17782656kB [root@nexus /etc]#
Add the metadevice to your /etc/iscsid.conf.
# 4 Disk Linux RAID Stripe
Target iqn.1997-06.com.homestead:storage.raid.stripe0
User
Lun 0 /dev/md0
Alias RAID0
If iSCSI is in use, stop both the initiator and the target daemons now.
[root@nexus /etc]# /etc/init.d/iscsi stop Stopping iSCSI: sync umount sync iscsid iscsi [root@nexus /etc]# /etc/init.d/iscsid stop Stopping iSCSI target.
Start the target daemon and then the initiator. Watch syslog while you do this to make sure your new target is auto-discovered.
[root@nexus /etc]# /etc/init.d/iscsid start Starting iSCSI target. [root@nexus /etc]# /etc/init.d/iscsi start Starting iSCSI: iscsi iscsid fsck/mount
In syslog (/var/log/messages) we see a new target auto-discovered.
kernel: scsi singledevice 1 0 2 0 kernel: Vendor: LINUX Model: ISCSI Rev: 0 kernel: Type: Direct-Access ANSI SCSI revision: 03 kernel: Attached scsi disk sdj at scsi1, channel 0, id 2, lun 0 kernel: SCSI device sdj: 142261248 512-byte hdwr sectors (72838 MB) kernel: sdj: unknown partition table
Now partition, label and create a filesystem on the new target.
[root@nexus /etc]# fdisk /dev/sdj ( Removed for Clarity ) Command (m for help): p Disk /dev/sdj: 64 heads, 32 sectors, 69463 cylinders Units = cylinders of 2048 * 512 bytes Device Boot Start End Blocks Id System Command (m for help): n Command action e extended p primary partition (1-4) p Partition number (1-4): 1 First cylinder (1-69463, default 1): Using default value 1 Last cylinder or +size or +sizeM or +sizeK (1-69463, default 69463): Using default value 69463 Command (m for help): p Disk /dev/sdj: 64 heads, 32 sectors, 69463 cylinders Units = cylinders of 2048 * 512 bytes Device Boot Start End Blocks Id System /dev/sdj1 1 69463 71130096 83 Linux Command (m for help): w The partition table has been altered! Calling ioctl() to re-read partition table. ( Removed for Clarity ) Syncing disks. [root@nexus /etc]# mkfs -t jfs /dev/sdj1 mkfs.jfs version 1.1.0, 20-Nov-2002 Warning! All data on device /dev/sdj1 will be lost! Continue? (Y/N) y \ Format completed successfully. 71130096 kilobytes total disk space.
Now mount it.
[root@nexus /]# mkdir /iscsi_raid [root@nexus /]# mount -t jfs /dev/sdj1 /iscsi_raid [root@nexus /]# df -h Filesystem Size Used Avail Use% Mounted on /dev/hda1 4.8G 4.3G 286M 94% / /dev/hda5 13G 11G 2.0G 85% /home /dev/sdj1 68G 8.7M 67G 1% /iscsi_raid
Done! Put some data on the new device and watch all the lights blink while you do writes, run some benchmarks, or just watch iostat data while you copy data onto the device.
[root@nexus benr]# iostat -kt
Linux 2.4.22 (nexus.homestead.com) 04/13/2004
( Removed for Clarity )
avg-cpu: %user %nice %sys %iowait %idle
7.00 0.00 50.00 0.00 43.00
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
dev3-0 205.00 8488.00 2248.00 8488 2248
dev8-0 0.00 0.00 0.00 0 0
dev8-1 0.00 0.00 0.00 0 0
dev8-2 0.00 0.00 0.00 0 0
dev8-3 122.00 0.00 3604.00 0 3604
dev8-4 120.00 0.00 3596.00 0 3596
dev8-5 121.00 0.00 3604.00 0 3604
dev8-6 122.00 0.00 3600.00 0 3600
dev8-7 0.00 0.00 0.00 0 0
dev8-8 0.00 0.00 0.00 0 0
dev8-9 126.00 0.00 14404.00 0 14404