Ronny Egners Blog

A few days before i posted a short howto how to configure iSCSI multipathing with Nexenta. This post covers the configuration of the linux initiator using iSCSI multipathing.

Before we start a preleminary note: It is a very good idea (i´d call it: “required”) to use separate subnets for each physical interface.  Do NOT use the same subnet accross different network interfaces!

If you do not comply with this simple rule you will end up having problems with so called Arp Flux (also documented here, here, here and so on) which requires further modifications.

For configuring and using iSCSI multipathing the following packages are needed:

• device-mapper-multipath
• device-mapper-multipath-libs
• iscsi-initiator-utils

Our testlab used a VM based on Oracle Enterprise Linux 6 Update 2 with two physical interfaces:

• eth1:    192.168.1.200/24
• eth3:    192.168.10.2/24

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File systems do have limits. Thats no surprise. ext3 had a limit at 16 TB file system size. If you needed more space you´d have to use another file system for instance XFS or JFS or spilt the capacity into multiple mount points.

ext4 was designed to allow far more larger file systems than ext3. According to wikipedia ext4 has a maximum file system size of 1 EiB (approx. one exabyte or 1024 TB).

Now if you´d try to create one single large file system with ext4 on every linux distribution out there (including OEL 6.1; as of 18th August 2011) you will end up with:

[root@localhost ~]# mkfs.ext4 /dev/iscsi/test mke4fs 1.41.9 (22-Aug-2009)
mkfs.ext4: Size of device /dev/iscsi/test too big to be expressed in 32 bit susing a blocksize of 4096.

This post is about how to solve the issue.

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