NAS (Network Attached Storage) and DAS (Direct Attached Storage) removable backup devices can have different speeds depending on the data rate of the interface as well as the speed of the device and hard drives being used.  The speeds below are backup to a single 2TB or 3TB type SATA drive. FirstRAID and RAIDFrame backup devices can be slightly faster due to the fact they use multiple drives in an array.

Direct Attached Storage or DAS refers to connecting storage directly to the server.  For Highly Reliable Systems our removable backup products use one of three types of DAS connection:

1. USB 2.0 (0.5 Gbps [480Mbps] data rate)   Backup speeds to SATA disk are up to 120 Gigabytes/Hr.
2. eSATA (3.0 Gbps data rate) Backup speeds to SATA disk are up to 460 Gigabytes/Hr.
3. USB 3.0  (4.8 Gbps data rate) Backup speeds to SATA disk are up to 440 Gigabytes/Hr.

Note the USB 3 port also supports USB 2 connections. From the data rates above, you might expect USB 3.0 to achieve the highest backup speeds but as you can see, USB 3.0 can be slightly slower than eSATA despite the higher data rate of the cable.  This is because the hard drives we use are native SATA and a bridge chip must be used to convert to USB 3.0, meaning the higher data rate doesn’t always mean faster backups.  However, any speed difference is usually negligible and USB 3.0 controllers are often more compatible with servers that may already contain a storage controller.  For this reason USB 3.0 can be the preferred interface if eSATA conflicts are encountered.

Network Attached Storage or NAS devices are attached to the network (as opposed to directly to the server), usually with a 1 Gigabit Ethernet card.  NAS devices are usually not quite as fast as DAS devices for backup.  However, NAS devices are more intelligent, do not require a dedicated controller in the server being backed up, and typically have a “motherboard” with CPU and RAM running an operating system that shares the hard drive using a higher level network protocol. The numbers below assume a standard 1500 byte ethernet frame (Jumbo frames and bonding or teaming multiple NICs can sometimes improve speed).

1. Gigabit Ethernet (1 Gbps data rate) and connected via a Windows Share – Backup speeds up to 180 Gigabytes/Hr.  Windows shares use the Server message Block or SMB protocol.
2.  Gigabit Ethernet (1 Gbps data rate) and connected via iSCSI– Backup speeds up to 300 Gigabytes/Hr.  iSCSI uses a low level block protocol that bypasses the network security and thus achieves faster speed.  However in our iSCSI implementations only ONE host being backed up attaches to each removable drive in the NAS.  While this drive can then be “re-shared” for other servers, doing that creates a potential slow down.
3. Gigabit Ethernet (1 Gbps data rate) and connected via NFS up to 240 Gigabytes/Hr.  NFS is a networking protocol like SMB that is typically used by Unix/Linux and VMWare systems.  It is easier to implement on these operating systems than SMB and has good speed.   Backup speed depends on many factors so your mileage will vary.