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Comparing iSCSI and Windows Shares

You can’t tell by looking whether a machine is using iSCSI or a Windows Share.  Both iSCSI and Windows Shared hard drives use an Ethernet connection to attach storage.  Since they use the same physical connection and cable, it can be confusing understanding the difference.  It used to be that an appliance that “shared” it’s drive was called a NAS (Network Attached Storage) and one that used iSCSI was called a SAN (Storage Area Network).  This was because  iSCSI was setup by installing a second network card in the server and a dedicated link or ethernet network was used for just storage traffic (hence the term storage area network versus local area network).  Now days it’s not uncommon for even low end NAS boxes to support the iSCSI software protocol so the line can be somewhat blurry.

In High-Rely’s current backup appliances, we allow drives to be used over ethernet via Windows Share (also called SMB or CIFS), NFS (the equivalent protocol often used in Linux or Unix), or iSCSI.   One thing to be aware of us that since we support removable disks, we typically use one of these protocols per drive.  In other words, if you turn on iSCSI to access a removable disk, the entire disk is accessed this way and no SMB shares are allowed on the drive.  This is to facilitate remove-ability and transportability.

Shared Drives.  Most network administrators are familiar with Windows network “shares”. When you use a network share, you’re dealing with whole files. The NAS device is responsible for creating the file system that stores the files, and presents those files to the clients. The NAS “server” is responsible for managing file permissions and security as well as contention should multiple clients try to access the share/file.

iSCSI Drives. Conversely, iSCSI is a block protocol. What ends up happening in this case is the NAS device creates a virtual disk file, and

Our iSCSI software allows for “safe removal” of network attached drives. Although not required, it insures all writes are complete

presents this disk to the client. The client is then responsible for creating the file system on the disk and modifying the contents. The NAS device will have no concept of what data is on the iSCSI disk, and relies on the clients to manage their own connections to it.  Because iSCSI eliminates overhead it is usually faster than a Windows Share.  It is also sometimes possible to boot from an iSCSI device.   Use iSCSI if you need to make a networked location appear as a local disk to one system and/or application.   iSCSI is really intended for one host connecting to the iSCSI target at a time. We don’t support multi-host mapping, as it’s usually used for fail over servers such as Windows clustering while we’re a backup device.  Although you can’t have 2 machines play nicely with iSCSI to our hard drives concurrently,  you can connect Server1 to a High-Rely drive via iSCSI then simply “share” that drive from Server1 to the rest of the network.   Although Server1 will have the fastest access to the drive, the other machines will then be able to backup to the drive as well.

Summary:

  • iSCSI is usually faster than Windows SMB/CIFS Shares.
  • Only one machine may connect iSCSI to one drive at a time. (although each drive may be “reshared” to the network”)
  • Each High-Rely drive must be shared either iSCSI, NFS, or Windows Share.  No mixing protocols per drive due to removable support.
  • If using NTFS file format (Windows native), better performance is achieved by connecting iSCSI and letting the Windows machine format the drive
  • When using EXT4 file format (Linux native), use NFS or Windows shares for best performance.
Darren McBride

About Darren McBride

CEO, Highly Reliable Systems, Inc. View all posts by Darren McBride →


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