White Paper - Data Protection In Novell Netware

White Paper: Data Protection In Novell Netware Date of publishing: 19th.October, 2004 Authored By: Product Engineering Group Version: 1.0 Novell Netware as an OS needs a basic bootable OS to work. So any Netware loaded hard disk contains two partitions at minimum, one is non-netware partition (for boot) and another is Netware partition. Data protection in Novell Netware refers to protection of data, which is there in NetWare partition. In overall, in Novell’s own terminology, data protection is referred as SFT (System Fault Tolerance). There are three different levels of SFT as briefed below. A higher level of SFT ensures decreasing possibility of data loss. SFT-I SFT-II SFT-III

: Disk Mirroring : Disk Duplexing (or, Controller Mirroring) : System Mirroring

Here below is an in-depth detail of these different levels and SFT in totality.

SFT System fault Tolerance (SFT) refers data duplication on multiple storage devices and thus keeps a level of redundancy. In case one device fails, data is available from other devices.

SFT-I : Disk Mirroring Disk Mirroring refers duplication of data from the NetWare partition on one hard disk to the NetWare partition on another hard disk. When you mirror disks, two or more hard disks on the same channel are paired. Blocks of data written to the original (primary) disk are also written to the duplicate (secondary) disk. The disks operate in tandem, constantly storing and updating the same files. If one of the disks fails, the other disk can continue to operate without data loss or interruption If one disk fails, the operating system sends a warning message to indicate the failure so that the mirroring protection can be restored as soon as possible.

Because disk mirroring duplicates disks on the same channel, it does not protect against failures that may occur along the channel between the disks and the file server. A problem in the channel may cause a failure in both disks and thus data loss.

Channel

Channels

Mirrored Disks

Mirrored Disks

Controller

Controllers

SFT-I : Mirroring

SFT-I I : Duplexing

SFT-II : Disk Duplexing Disk duplexing consists of copying data onto two hard disks, each on a separate disk channel. Each Disk channel is connected to individual disk controller and interface cable. This protects data against the failure of a hard disk or failure of the hard disk channel. The hard disk channel includes the disk controller and interface cable. If any component on one channel fails (Disk, Cable or Controller), the other disk can continue to operate without data loss or interruption, because it is on a different channel (different Disk, different Cable, different Controller). Disk duplexing allows the same data to be written to all disks simultaneously.

Since the disks are on different channels, data transfer is faster than with disk mirroring, where data is written to the disks sequentially over the same channel. Disk duplexing also allows split seeks: read requests are sent to whichever disk can respond first. Multiple read requests are also split between the duplexed disks for simultaneous processing. Duplexing alone doesn't guarantee data protection. If both disk channels fail at the same time, or if the computer itself fails, you still lose your data.

SFT-III : System Mirroring The problem with disk Duplexing is if the server itself fails, the data is not available. System Mirroring ensures data availability in such scenario. In fact in SFT-III a complete system including it’s HDD, controller, communication and even memory writes and reads also are mirrored. This is very high level of redundancy, which ensures data availability in case of disk failure, cable failure, controller failure, memory failure or even the total system failure. The implementation calls for two absolutely identical systems from Disk, controller, and system perspectives. As well this calls for special MSL cards (Mirror server Link) to ensure online synchronization of two systems.

Mirrored Systems

Mirrored Disks Controllers MSL Cards

SFT-I I I : System Mirroring

Mirroring and Duplexing are supported in Netware 4.11 till Netware 6.5 SFT-III is supported in Netware 4.2 only. So, as on date, Mirroring and Duplexing are supported by Novell; but not SFT-III. Instead Novell supports clustering, which is more of a complete solution like MSCS rather than system specific application independent implementation on OS layer.

References: http://www.novell.com/documentation/nw6p/index.html?page=/documentation/nw 6p/sdiskenu/data/hefkruob.html http://www.novell.com/documentation/nw312/docui/index.html#../cncptenu/data/f m56742.html http://searchstorage.techtarget.com/sDefinition/0,,sid5_gci796504,00.html