Network direct attached storage
Network Direct Attached Storage ( NDAS ) is a proprietary technology for connecting external storage media such as hard drives , flash memories or tape drives to a network . NDAS devices are connected directly to an Ethernet cable. The storage media appear on the target system like local data carriers. NDAS systems use the network protocol LPX (Lean Packet Exchange), a proprietary protocol developed by Ximeta that is not based on the TCP / IP standard. The American manufacturer IOCELL Networks has held the rights to the NDAS technology since August 2011.
Structure and technology
NDAS storage systems usually consist of at least one external housing for one or more hard drives. Control electronics are integrated into the housing, which control the network and possibly other interfaces and regulate the provision of data in the network. There is also a power supply unit for power supply.
LPX protocol
The external storage media are connected to the clients using a proprietary network protocol called LPX (Lean Packet Exchange). LPX is only forwarded by switches (or hubs ). TCP / IP routing , i.e. forwarding to other subnets via a router , is consequently not possible. The advantage of this implementation is the low overhead and the low system requirements (computing power, memory) of the LPX protocol. This results in a comparably high data throughput, especially with power-saving and therefore low-performance CPUs , as are often used in inexpensive and particularly 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 data carriers can be connected to switches , WLAN access points or WLAN routers via Ethernet cables and thus made available to one or more computers in the network.
Many NDAS systems for end users are also equipped with a USB 2.0, eSATA or (less often) Firewire connection so that the hard disk or the hard disk network system can also be connected to the computer as a local external mass storage device . NDAS properties are then switched off.
WiFi and routing
Manufacturers usually advise against connecting the NDAS via WLAN , just as it is pointed out that no access is possible "via the Internet". Hubs are also not recommended. In terms of network technology, this can be interpreted in such a way that the LPX protocol is generally not routable .
In practice this means that all devices - NDAS as well as target systems - can only be operated in local, non-routed networks.
Comparison with NAS
Functionality
NDAS storage media at rest in a SOHO environment storage ready, but not beyond server functionality such as DHCP , FTP , media streaming , own user management etc., as in network attached storage has become conventional (NAS). Initial error when accessed via DSL - routers now lodged with the NDAS systems is no longer a problem (as of January 2008), but all clients must remain in the same network segment are (in October 2008, Ximeta: ... Only computers under the same subnet can even attempt to connect to the Netdisk ... ).
Since NDAS volumes appear like local volumes from the operating system's point of view, they can be formatted with local file systems such as NTFS , HFS + or others (with all the advantages and disadvantages of these file systems) as opposed to the file system of a NAS file server. Therefore the data backup via TimeMachine from Mac OS X (Leopard) also works perfectly with NDAS.
The number of simultaneous users is named differently depending on the source: According to the company Ximeta , a maximum of 64 parallel users are possible, but in practice a maximum of 16 simultaneous users is recommended.
RAID
Most NDAS systems now offer RAID levels 0 and 1. While RAID 1 increases reliability by mirroring two hard disks , RAID 0 can increase throughput - but at the expense of reliability. The RAID array can be spanned across the network on two spatially distributed disks. In the event of an error, older implementations or drivers may require more effort, that is, a backup of the remaining disk must be created and then both hard disks must be reformatted. RAID level 5 was announced on the Ximeta website for around mid-2007.
performance
The data transfer rate is potentially better with NDAS systems than with Network Attached Storage (NAS) devices. Because NAS devices usually a mini Linux as operating system use and connection via TCP / IP or FTP and SMB need are at NAS devices reduces the available bandwidth on the network and more heavily loaded CPU and network card chipset.
Since NDAS media appear like local hard disks on the systems connected to them, even if they are actually integrated via the network, processes that are normally only executed locally can slow down all connected PC or server systems. Examples are changes to the file attributes or NTFS rights, the Windows index service, or defragmentation.
Based on user reports, Ximeta advises against routed WLAN sections in the network, 10 Mbit networks, hubs in the network, and more than one basic partition per NDAS system.
Supported operating systems and file systems
Ximeta supports the operating systems Windows 98SE / 2000 / XP / 2003 / Vista / 2008/7, various Linux kernel and Mac OS X . As of Mac OS X 10.6.7 (March 2011) and Windows 10 , the Ximeta driver no longer works, a fix has been promised, but has not yet been redeemed.
The Windows drivers of version 2.x only work together with the FAT32 file system , while the drivers of version 3.x also support NTFS . Under Windows, the NDAS device can be used jointly by several computers in the network, both for reading and writing.
Mac OS X supports HFS , HFS +, and HFSX () file systems .
The Linux driver supports all file systems commonly used for hard drives (e.g. ext2 , ext3 , FAT32, NTFS), but not shared write access by multiple computers. Cluster file systems such as the Global File System , OCFS2 or the Veritas File System must be used for shared write access to the NDAS device . Otherwise, there is a risk of file system damage and data loss.
handling
While with NAS you sometimes have a little more effort with the user administration and configuration - but usually only once - with NDAS there is a corresponding effort with the driver installation for every PC that should be able to access, as well as for every user of a computer, to which only restrictive access rights have been assigned (this is basically the basic problem of Windows workgroups without central user administration).
Device implementations
All devices on the market that implement NDAS technology are based on controllers from Ximeta or IOCELL and use the proprietary driver software developed by these companies . The devices originally offered by Ximeta and still today by the patent holder IOCELL are marketed under the NETDISK brand. Different equipped models are on offer. In addition to IOCELL, other companies also act as device providers, such as Dawicontrol GmbH from Göttingen and SHARKOON Technologies Ltd. from Taiwan .
See also
Individual evidence
- ↑ Joseph F. Kovar: IOCELL Acquires Ximeta's SOHO, SMB Storage Technology In: CRN Magazine , August 8, 2011.
Web links
- IOCELL Networks: What is NDAS? - Technology description
- the Linux driver sources for version 1.1.24 (June 30, 2008)