iSCSI

iSCSI Terms

An iSCSI initiator is something that requests disk blocks, aka a client

An iSCSI target is something that provides disk blocks, aka a server.

An iSCSI portal is the combination of the IP and Port of a target

Terms

Target

Portal:172.20.81.5/3260

Linux box, providing adisk as an iSCSI target

Initiator

Windows/Linux/OSX box,Mounting the target asA block device

Terms

In this case, the target is a linux box running the iSCSI daemon. The IP and the port the daemon are listening on are the portal. Any device that can act as an iSCSI initiator can connect to the portal and treat the device as a block device

The space served by the target is a raw disk device

iSCSI Setup

On the server side, setup is still somewhat nasty.iSCSItarget.sourceforge.net has a linux

implementation of iSCSIYou need to recompile the kernel; kernel 2.6 or

more recent is requiredYum update kernel kernel-devel to get the

necessary filesExport KERNELSRC=/usr/src/kernes/2.6.14…Make, make installInit scripts installed in /etc/rc.d, /etc/init.d

iSCSI Target

Target address format:Iqn.2004-04.edu.nps:storage.something.here“iqn” is the type (iSCSI Qualified Name)2004-04 is the date of the first full month the

naming authority was registeredEdu.nps is the reversed domain name, the

naming authorityStorage.something.here is a name assigned by

youBasically, you only have to worry about the last

field

Etc config

In /etc. ietd.conf controls nameTarget iqn.2001-

04.iscsi.ern.ps.edu:storage.iscsi.fileLun 0 Path=/dev/sdb/etc/iscsi has some other config

parameters

Client Side (Initiator)

Now that the target (provider of disk space) is set up we can configure the client.

On Windows, get the MS iscsi initiator (google) and run the installer

Start iSCSI initiator and specify the IP and port to connect to

Discovery/Portals

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Targets

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Note that the namematches the name weprovided in the ietd.conffile--we connected successfully

Disk

At this point we have block device access to the device. On another system I created a FAT filesystem, so we can also show this as a FAT drive.

NOTE: If two machines have block access, they WILL eventually put the FAT filesystem into an inconsistent state. Ditto for ext, zfs, ntfs, and other single-host filesystems

iSCSI on OSX

Supposedly iSCSI was going to be part of Leopard--it didn’t make it. Probably be added at some later date

There are free iSCSI initiators available, http://www.studionetworksolutions.com

Run installer; adds a .kext kernel extension, which requires a reboot

globalSAN

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Note IP and 3260 port

GlobalSan

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Connection established;note match of iscsi ID with that of thetarget config file

Filesystem Creation

Once you have access to the iSCSI drive as a block device, you can create a filesystem on the device.

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Filesystems

Again, conventional filesystems are designed to have only one OS access them as a block device.

We can have multiple hosts contact the iSCSI block device. A conventional filesystem will eventually become inconsistent if you do writes from multiple hosts

What did we get?

We accessed a block device on a linux server from OSX and Windows across an IP network using commodity ethernet (or wireless) protocols.

This isn’t quite a SAN, since we don’t have volume management, but it provides the substrata needed for that

Volume Management

This is somewhat tricky and still a developing field. There are a number of commercial implementations and a few open source implementations

This is the layer that handles concurrent access to block devices

Architecture

What would a cluster architecture look like with a SAN?

iSCSI devices

No endorsement implied by any mention of a vendor, prices variable….

Promise vtrack: ~$5K for enclosure, plus disk

16 SATA bays, 3U, RAID, TCP Offload Engine

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iSCSI Devices

HP Storage Works AIO 1200, 600, 400SATA or SAS drives possiblehttp://h18006.www1.hp.com/storage/aiostorage.html?jumpid=reg_R1002_USEN~ $8K for 3 TB

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iSCSI

Sun is generally dismissive of iSCSI for their enterprise storage products

EMC has an installed base in FC, though they do offer iSCSI in parallel on some boxes

EMC is partnered with Dell: AX150 (12 SATA drives, 9 TB, RAID) $11K for 1.5TB (Massive discounts probably apply)

CX3 series: up to 144TB, enterprise stuff