Page 273 -

P
244
244 P a r t V : a r t V : T T h e G r e e n i n g P r o c e s sh e G r e e n i n g P r o c e s s

Software Some software implementations are complicated to design and code. For example,
network-based and in-band designs are especially complicated, so read and write requests
can lead to latency problems.

NOTE We talk more about network-based and in-band designs later in this chapter.
Metadata Management
When you write data to your hard drive, you don’t know exactly where, on your drive, it is
stored. A piece goes here, a piece goes there. If you have to find the information, it is possible,
albeit a hassle.
In a storage virtualized environment, not only is data scattered throughout a drive,
it’s scattered throughout several drives. The only way to know where everything is comes
down to the metadata. The metadata is sort of the map your system uses to find data.
As such, if something happens to the metadata—while still located on your drives—for
all intents and purposes, the data is gone.

METADATA
1001 01011 0011
0010 00110 0110101
01010 1010 0101
0101
The metadata is a list of
where data is stored on
your SAN’s drives. If the
list is lost, the data
remains, but it cannot be
found.
Disk drives

Because metadata is so important, it is critical that the metadata is backed up and kept
safe. But not only must metadata be recoverable, it must be updated quickly. If a file is
saved on the system and others need to access it, that metadata must be updated so others
can find the file.
Performance
You may also experience some performance problems if the system isn’t properly tuned.
Caching required data must be visible to input/output (I/O) requests. If the I/O request
misses cached data, there is a performance hit as the request tries to relocate the data. If the
software or the device is efficiently designed and tuned, this shouldn’t be a problem, but it
can be if the system is not properly optimized.

NOTE It’s not all bad news. You may also see a performance increase when the system is put
together properly.