1. What is storage?
The memory where
we can store the data, such as files,
directories, ...etc., is called
the storage. Storage is mainly two
types. (i) Local
storage and (ii)
Remote Storage.
(i) Local storage :
Local storage is a storage which is directly
connected to our system and ready to use.
Example : Local hard disk, local pen drive, DAS (Direct
Access Storage) ... etc.,
(ii) Remote storage :
The
storage which is not connected to our system directly but allotted some space
to our system in remote location
is called remote storage.
Example : iSCSI
(Internet Small Computer
System Interface), SAN (Storage Area Network), NAS (Network Area Storage)
2. What is iSCSI and
explain it?
iSCSI
is a way of connecting storage devices over a network using TCP/IP. It can be
used over a local area network
(LAN), a wide area network (WAN), or the Internet.
iSCSI
devices are disks, tapes, CDs, and other storage devices on another networked
computer that you can connect to.
Sometimes these storage devices are part of a network called a Storage Area Network (SAN).
In
the relationship between our computer and the storage device, our computer is called an initiator because it
initiates the connection to the device, which is called a target.
iSCSI provides Remote Block or
File Storage. Most data centers
keep their storage in centralised
SAN racks. iSCSI provides
an inexpensive alternative to
proprietary SAN hardware.
3. What is the
terminology of iSCSI?
iSCSI supports sending SCSI
commands from clients
(initiators) over IP to
SCSI storage devices
(targets) on remote systems
(servers). iqn is a iSCSI
qualified name or number.
The
format of iqn is "iqn.yyyy-mm.
4. What is the
profile of iSCSI?
Package : iscsi* (for
RHEL-6), target* (for RHEL-7 server) and iscsi-utils* (for RHEL-7 Client)
Configuration files : /etc/tgt/target.conf (for
RHEL - 6) and /etc/target/saveconfig.json (for
RHEL - 7)
Deamons : tgtd (for
RHEL-6) and target (for
RHEL-7 server) and iscsi, iscsid
(for RHEL-7)
Port
number : 3260
5. How to configure
the iSCSI server?
(i) Create one partition and
create the LVM with that partition.
# fdisk
: n
(new partition) ---> Enter
---> Enter --->
Enter ---> + ---> w
(write the changes into the disk)
#
partprobe (to write the changes into the partition table)
# pvcreate
# vgcreate
# lvcreate
-s -n
(to create the logical
volume)
(ii) Install the iSCSI
package by #
yum install scsi-target-utils -y command
in RHEL - 6 or
Install
the iSCSI package
by # yum install target*
-y command in
RHEL - 7.
(iii)
Start the iSCSI deamon
and enable the deamon at next boot time.
# service
tgtd restart (to start the iSCSI deamon in
RHEL - 6)
#
chkconfig tgtd on (to enable the iSCSI
deamon at next boot in RHEL - 6)
#
systemctl start target (to
start the target deamon in RHEL - 7)
#
systemctl enable target
(to enable the target deamon at next
boot in
RHEL - 7)
(iv)
Configure the iSCSI storage.
In
RHEL - 6 :
#vi
/etc/tgt/targets.conf
default-driver iscsi
backing-store
write-cache off
In
RHEL - 7 :
# targetcli (to get the configuration window and
displays "/>"
prompt appears)
/> ls (to
see the configuration contents)
/> /backstores/block create
(create the block storage)
/> /iscsi
create iqn.2015-06.com.example:server9
(to create the lun number not the
lun name)
/>
/iscsi/iqn.2015-06.com.example:server9/tpg1/acls create
iqn.2015-06.com.example:server9 (to create the alias name for client
side lun number)
/>
/iscsi/iqn.2015-06.com.example:server9/tpg1/luns create
/backstores/block/
(to
create the lun using the block storage device)
/>
/iscsi/iqn.2015-06.com.example:server9/tpg1/portals create
(to allot the above created lun to
the IP address and
port number, ie., 3260)
/> saveconfig (to save the iSCSI
configuration into the configuration
file)
/> exit (to exit from the configuration window)
(v) Restart the iSCSI
deamons after the
configuration of iSCSI
or target.
# service
tgtd restart (to start the iSCSI deamon in
RHEL - 6)
#
chkconfig tgtd on (to enable the iSCSI
deamon at next boot in RHEL - 6)
#
systemctl restart target (to
start the target deamon in RHEL - 7)
#
systemctl enable target
(to enable the target deamon at next
boot in
RHEL - 7)
(vi)
# tgt-admin --show (to
check the iSCSI configuration in RHEL - 6)
(vii)
Add the iSCSI service
and port number to the IP tables
and firewall.
In
RHEL - 6 :
# iptables-I INPUT -p tcp-m tcp
--dport3260 -jACCEPT
# iptables-O OUTPUT
-p tcp-m tcp --dport3260 -jACCEPT
#
service iptables save
#
service iptables restart
In RHEL - 7 :
#
firewall-cmd --permanent --add-port=3260/tcp
#
firewall-cmd --complete-reload
6. How to configure the iSCSI
client?
(i) Install iscsi-initiator-utils package on the client by # yum install
iscsi-initiator-utils* -y command in RHEL-6.
Install
the iSCSI packages by # yum
install iscsi-utils* -y
command in RHEL - 7.
(ii) Discover the target
LUN’s exported by server using following command. It will provide iqn name with
of LUN associated
with given ip address.
# iscsiadm -m discovery -t sendtargets -p
# iscsiadm --mode
discoverydb --type sendtargets
--portals (in RHEL - 7)
(iii) Open the
iscsi initiator file and
put an entry of the above discovered
lun number in RHEL - 7 only.
# vim /etc/iscsi/initiatorname.iscsi (go to last line and type as below)
Initiatorname=iqn.2015-06.com.example:server9 (save
and exit this
file)
(iv) Restart
and enable the
iSCSI client side deamons.
# service iscsi
restart (to restart the iscsi
client deamon in RHEL - 6)
#
chkconfig iscsi on (to
enable the iscsi client deamon at next boot
in RHEL - 6)
#
systemctl restart iscsid
iscsi (to restart the iscsi
client deamons in RHEL - 7)
#
systemctl enable iscsid
iscsi
(to enable the iscsi client deamons at next boot in
RHEL - 7)
(v) To connect iSCSI target we can use following command , we need to
mention server ip and iqn name.
In
RHEL - 6 :
#
iscsiadm -m node -T iqn.2015-06.com.example:server9.target1–p login
In RHEL - 7 :
#
iscsiadm --mode node
--targetname
iqn.2015-06.com.example:server9
--portal : 3260 --login
(vi) Check the new remote disk name by #
fdisk -l command.
(vii) Create the required size partition using # fdisk, # partprobe commands.
(viii) Create the required type of file systems by #
mkfs.ext4
(ix) Create a mount point for the above file
system by # mkdir
/mnt/iscsi command.
(x) Open
the /etc/fstab file
and put en entry of the above file system information.
# vim /etc/fstab
(xi) Mount the all the partitions which are having
entries in /etc/fstab file
by # mount -a
command.
(xii) Check all the mounted file systems by #
df -hT command.
(xiii) To disconnect iSCSI
target we can use following commands.
Don't forget that logout from the
target.
In
RHEL - 6 :
#
iscsiadm -m node -T iqn.2015-06.com.example:server9.target1–p logout
In RHEL - 7 :
#
iscsiadm --mode node
--targetname
iqn.2015-06.com.example:server9
--portal : 3260 --logout
(xiv) Restart the client system by #
init 6 command.
(xv) After reboot
check the remote file system
by # df -hT
command.
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