Network Direct Attached Storage

Network Direct Attached Storage ( NDAS ) is a proprietary technology for connecting external storage devices like hard disks, flash memory or tape drives to a network. NDAS devices are connected directly to an Ethernet cable. The storage media appear on the target system, such as local disk. NDAS systems use the network protocol LPX ( Lean Packet Exchange ), a proprietary protocol developed by Ximeta protocol that is not based on the TCP / IP standard. The rights to the NDAS technology holds since August 2011, the American manufacturer IOCELL Networks.

Construction and Technology

NDAS storage systems usually consist of at least an external enclosure for one or more disks. Into the housing, control electronics are integrated, which controls the network and possibly present, additional interfaces and regulates the provision of data on the network. Added to this is an AC adapter for power supply.

LPX protocol

The external storage devices can be connected using a proprietary network protocol called LPX ( Lean Packet Exchange ) to the clients. LPX is forwarded by switches (or hubs). A TCP / IP routing, ie routing to other subnets through a router, is therefore not possible. The advantage of this implementation is its low overhead, and in the low system requirements ( processing power, memory ) of the LPX protocol. This results in a comparable high data throughput, especially for low-power and low-power CPUs, therefore, as they are often used in low-cost and highly mobile (small) devices. This technique is similar to AoE. The connection of the clients is realized by a driver program (available for Windows 95/98/Me/2000/XP/Vista/7, Mac OS 10.2, Linux), which integrates the NDAS as a virtual SCSI drive.

Cabling

NDAS disks can be connected via Ethernet cable to switches, wireless access points or wireless routers and as provided for one to several computers on the network.

Many NDAS systems for Endbenutzerbereich are also equipped with a USB 2.0, eSATA or (more rarely) Firewire port, so that the hard disk or the hard disk composite system can also be connected as a local external mass storage on a computer. NDAS properties, however, are then switched off.

Wi-Fi and routing

From the connection of the NDAS over WLAN is not recommended by the manufacturers usually, as pointed out is that no access is possible " on the Internet ". Likewise, it is not recommended hubs. One can interpret network technology so that the protocol LPX is generally not routable.

In practice, this means that all devices - NDAS as well as target systems - can be operated in local, non-routed networks.

Comparison with NAS

Functionality

NDAS storage devices provide, but no beyond server functionality such as DHCP, FTP, media streaming, own user management, etc., as is already the norm in Network Attached Storage (NAS ) in a SOHO environment storage capacity. Initial error when accessing via DSL router lodged with the NDAS systems now no longer a problem (as of January 2008), but all clients must still be in the same network segment (October 2008 Ximeta: ... Only computers under the same subnet can even attempt to connect to the Netdisk ... ).

Since NDAS disks appear from the perspective of the operating system such as local disks, they can with local file systems are formatted other as NTFS, HFS or - with all the advantages and disadvantages of these file systems, as opposed to the file system of a NAS file server. Therefore, the backup system Time Machine in Mac OS X ( Leopard) works flawlessly with NDAS.

The number of concurrent users is named differently depending on the source: According to the company Ximeta maximum of 64 concurrent users are possible, in practice, however, advised to a maximum of 16 concurrent users.

RAID

By now, most NDAS systems offer RAID levels 0 and 1. While RAID 1 increased by mirroring two disks fault tolerance, RAID 0 can increase the throughput - at the expense of reliability. The RAID array can be clamped on two spatially distributed disks over the network. In case of error may be necessary in older implementations or drivers of increased costs, in the form of backup from the remaining disks and subsequent reformatting of both plates. RAID level 5 is announced on the website Ximeta for about mid-2007.

Performance

The speed of data transfer is potentially better than Network Attached Storage (NAS ) devices with NDAS systems. Because NAS devices usually use a mini- Linux as the operating system and need a connection via TCP / IP or FTP and SMB in NAS devices, the available bandwidth is reduced on the network and CPU load and network cards chipset stronger.

Since NDAS media like local disks appear on their associated systems, even if they are integrated effectively across the network, processes that are normally performed only locally, slow down all the connected PC or server systems. Examples are changes to the file attributes or NTFS permissions, the Windows Indexing Service, or defragmentation.

Based on user reports advises Ximeta of routed wireless hops in the network, 10 -Mbps networks, the hubs in the network, as well as from more than one base partition per NDAS system from.

Supported operating and file systems

Ximeta supports the operating systems Windows 98SE/2000/XP/2003/Vista/2008/7, various Linux kernel and Mac OS X. Starting with Mac OS X 10.6.7 (March 2011) no longer works the Ximeta driver, a fix was in provided a view, but not yet redeemed.

The Windows driver version 2.x only work together with the FAT32 file system, while the driver version 3.x also support NTFS. On Windows, the common use of the NDAS device is among computers on the network both reading as well as writing possible.

Under Mac OS X, the file systems HFS, HFS , HFSX and () are supported.

Although the Linux driver supports all standard hard drives for file systems (eg ext2, ext3, FAT32, NTFS ), but not the shared write access by multiple computers. Need for shared write access to the NDAS device here cluster file systems such as the Global File System, OCFS2 or the Veritas File System can be used. Otherwise, the risk of damage of the file system and data loss.

Handling

While at NAS sometimes a bit more effort with the user management and configuration produced - but usually only once - so there is at NDAS a corresponding effort with the driver installation on every PC that can access to, as well as for each user of a computer, the only restrictive access rights assigned (that is, in principle, the basic problem of Windows Workgroups without a central user administration).

Device implementations

All devices on the market that implement the NDAS technology, based on controllers from Ximeta or IOCELL and use developed by these companies, proprietary driver software. The units originally offered by Ximeta and today by the patentee IOCELL even be marketed under the brand NetDISK. Differently equipped models are on offer. As equipment vendors come next IOCELL other companies on, about the Dawicontrol GmbH in Göttingen and the Sharkoon Technologies Ltd.. from Taiwan.