Netgear SC101T SC101T Reference Manual - Page 55

New Technology File System (NTFS), SAN and Network Attached Storage (NAS)

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Storage Central Turbo Model SC101T and Storage Central Model SC101 User Manual The SFS accesses hard disks by addressing entire extents, which are flexibly-sized groups of blocks. With a good disk allocator such as ours, extent-based file systems minimize fragmentation. For example, say Windows makes 64 KB requests for buffered I/O, which results in eight I/O requests for 8 KB blocks. The SC101 SFS allocator, in comparison, searches chunks of thirty-two 8KB blocks (before moving to sixteen 8KB blocks, before finally moving to eight 8KB blocks). Often files are larger than the maximum Windows request size, so Windows' files will fragment. SFS avoids the fragmentation of Windows. The SFS allocator can use both first-fit and best-fit algorithms, and typically outperforms Windows in terms of maximum blocks that can be transferred at a time. All this makes it easy for the SC101 to stay "defragmented", using its own software. Another non-Windows feature that reduces Storage Central disk accesses is stuffed dinodes. In the Windows NTFS disk management, the addresses for blocks are stored in a different place than the blocks, themselves. This means that any request for NTFS disk data, no matter how small, causes two I/O operations. Since hard disk I/O is far slower than your CPU or RAM, doubling the amount of I/O can have a noticeable impact on performance. Since SFS can store both the address and the data in the same extent, the amount of I/O for very small files is cut in half. New Technology File System (NTFS) With conventional disk management such the NTFS used by Windows, disks are divided into small, equally-size divisions called clusters; disk access is made for clusters, and a file may use many clusters. This old practice is suited for programs with limited needs for disk performance, or for low-level programs that handled their own disk access. Unfortunately, neither of these is true of many modern software applications. To reduce request fragmentation for large requests, Self-certifying File System (SFS) bypasses the Windows buffer cache and tries to make one request for the entire amount of data. See "SelfCertifying File System (SFS)" on page A-2. SAN and Network Attached Storage (NAS) The Storage Central is a SAN device. SAN disks run as an extension of a computer's operating system. Computers that use the Storage Central must have operating systems and software that are compatible with the SAN. A NAS is a more complicated device that has its own, small operating system. Sometimes computers that have been converted just to be file servers are referred to as NAS devices. Both technologies create disks that are accessed directly by many computers over a network. The computers share the network resource. This reduces maintenance in large systems, and also avoids having a single computer tied up answering requests for its data from all over a network. A-3 v1.0, December 2006

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Storage Central Turbo Model SC101T and Storage Central Model SC101 User Manual
A-3
v1.0, December 2006
The SFS accesses hard disks by addressing entire extents, which are flexibly-sized groups of
blocks. With a good disk allocator such as ours, extent-based file systems minimize fragmentation.
For example, say Windows makes 64 KB requests for buffered I/O, which results in eight I/O
requests for 8 KB blocks. The SC101 SFS allocator, in comparison, searches chunks of thirty-two
8KB blocks (before moving to sixteen 8KB blocks, before finally moving to eight 8KB blocks).
Often files are larger than the maximum Windows request size, so Windows’ files will fragment.
SFS avoids the fragmentation of Windows. The SFS allocator can use both first-fit and best-fit
algorithms, and typically outperforms Windows in terms of maximum blocks that can be
transferred at a time. All this makes it easy for the SC101 to stay “defragmented”, using its own
software.
Another non-Windows feature that reduces Storage Central disk accesses is stuffed dinodes. In the
Windows NTFS disk management, the addresses for blocks are stored in a different place than the
blocks, themselves. This means that any request for NTFS disk data, no matter how small, causes
two I/O operations. Since hard disk I/O is far slower than your CPU or RAM, doubling the amount
of I/O can have a noticeable impact on performance. Since SFS can store both the address and the
data in the same extent, the amount of I/O for very small files is cut in half.
New Technology File System (NTFS)
With conventional disk management such the NTFS used by Windows, disks are divided into
small, equally-size divisions called clusters; disk access is made for clusters, and a file may use
many clusters. This old practice is suited for programs with limited needs for disk performance, or
for low-level programs that handled their own disk access. Unfortunately, neither of these is true of
many modern software applications.
To reduce request fragmentation for large requests, Self-certifying File System (SFS) bypasses the
Windows buffer cache and tries to make one request for the entire amount of data. See
“Self-
Certifying File System (SFS)” on page A-2
.
SAN and Network Attached Storage (NAS)
The Storage Central is a SAN device. SAN disks run as an extension of a computer’s operating
system. Computers that use the Storage Central must have operating systems and software that are
compatible with the SAN.
A NAS is a more complicated device that has its own, small operating system. Sometimes
computers that have been converted just to be file servers are referred to as NAS devices.
Both technologies create disks that are accessed directly by many computers over a network. The
computers share the network resource. This reduces maintenance in large systems, and also avoids
having a single computer tied up answering requests for its data from all over a network.