Backup & Recovery

- iSCSI Background -

Considering the lifespan of iSCSI when compared to standard SCSI or Fibre Channel, it's not uncommon for people to be unfamiliar with the proper configuration and speed expectations of the new protocol.

iSCSI is an IP based standard that uses the 1Gb/s and 10Gb/s Ethernet standards to transfer data.   Many newer SANs have opted to use iSCSI instead of the costlier Fibre Channel.  
 

- Recommended iSCSI setups -
 

There are two ways to operate an iSCSI network:

  1.  iSCSI can be set up on it's own separate disjoint network using standard IP networking hardware utilizing multiple NICs available on most servers.
  2. The data can run through an existing multipurpose network setup using existing IP network hardware.
I generally recommend using the following NICs with an iSCSI infrastructure:
  • A server NIC w/ ToE (TCP/IP Offload Engine)
  • An iSCSI HBA (Host Bus Adapter), which is a combination of a standard server NIC, ToE and a SCSI bus adapter.


- Real World Data -

 

From my personal experience, I have compiled my average real-world backup speeds to an LTO3 tape drive that I've been able to achieve when backing up over iSCSI on a 1Gb/s network:

Backing up Exchange Mail stores (disjoint / low-traffic network):  Average of 30-50 MB/sec / 1.7-2.9 GB/min / 102-174 GB/hr
Backing up Exchange Mail stores (multipurpose network):  Average of 20-40 MB/sec / 1.2-2.3 GB/min / 72-138 GB/hr

Backing up File Servers (disjoint / low-traffic network):  Average of 25-60 MB/sec / 1.4-3.5 GB/min / 84-210 GB/hr
Backing up File Servers (multipurpose network):  Average of 15-40 MB/sec / 0.8-2.3 GB/min / 48-138 GB/hr

Obviously, depending on the size of your Exchange mail stores and the sizes and types of files on your File Servers can alter the backup speeds that you can achieve.

 

- Conclusion -

Since it's first uses in 2002 and more recent inclusion in modern SANs and Operating Systems, iSCSI has become a viable alternative to Fibre Channel for larger and smaller companies alike.   iSCSI's transfer rates are comparable to other current data transfer technologies and can achieve it at a fraction of the cost and with existing network hardware.   For companies looking to move away from Fibre or trying to incorporate networked storage at lower cost, iSCSI is an excellent option.
Comments
did you see an impact on the overall network performance when backing up over iSCSI or is the iSCSI network isolated on its own VLAN?
In general, best practice is to separate the iSCSI network from your main network using a different subnet and a VLAN.   In that case, there will be minimal impact on a typical 100Mb or Gigabit network during backup.  

If all of your iSCSI devices are connected through their own switch, you'll see virtually no disruption to overall network performance.