Re: does Vista limit use of SSD's?
- From: "Soundhaspriority" <nowhere@xxxxxxxxxxx>
- Date: Thu, 24 Jul 2008 07:34:46 -0400
"Jeff Wexler" <jw@xxxxxxxxxxx> wrote in message
news:jw-F635FD.20432623072008@xxxxxxxxxxxxxxxxxxx
I read this article and I didn't quite understand it. Is there somethingJeff,
in Vista that prevents it from using an SSD drive effectively?
quoting:
"SanDisk: Vista Shortfalls Limit Use of SSDs
by John Martellaro, 3:15 PM EDT, July 23rd, 2008
Problems have been previously noted with the NTFS file system and flash.
The Vista problems may be an extension of this.
Individual cells in flash memory have a lifetime limited by the number
of writes. In order to produce a flash memory with a usable lifetime, the
physical cells are constantly remapped by an internal algorithm. The process
is referred to as "load leveling." When a flash device is formatted with the
FAT file system, this works well, producing continuous write lifetimes on
the order of 30 years, based on continuous sequential write of the drive. It
works because FAT buffers the blocks in a sequential write, writing only
when the block is full.
But NTFS is a journaling file system. The journal entries are small
writes, "random writes", that serve as verification that individual blocks
were actually written. Journaling was a great advance in file system
reliability. When a computer that uses NTFS has a power failure, there is
usually no file system damage, and journaling is the reason why. However,
journaling creates a problem with flash memories. The kind of flash used in
SSD's is NAND, which is organized into blocks. Only complete blocks can be
accessed. When a journal write of a few bytes is made, the entire block
within which it is contained must be rewritten. This vastly accelerates the
wear of flash cells over sequential write, because it completely defeats the
load-leveling algorithm.
File systems are very complex. There is plenty of room for advances. For
example, while the XP version of NTFS protects the data till it gets to the
drive, modern drives have large internal caches. If the power is cut while
the drive is still writing data from the internal cache, file system
corruption results. The solution is to increase the number of journal
entries to reflect information that the drive provides to the OS about the
state of the internal cache. But this increases the number of random
writes, which makes an SSD wear out even further.
If the frequency of random writes in the Vista version of NTFS than it
is with XP, the problems of flash drives are accentuated.
Bob Morein
(310) 237-6511
.
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