Storage Networking Architectures
Limitations of DAS:
A SCSI bus can support only 16 devices, limiting the amount of storage
that can be directly attached. It is possible to attach multiple SCSI buses
to a host, but storage capacity is limited to a few dozen drives at most.
Adding more storage capacity, therefore, requires adding more servers.
This substantially increases the cost of storage.
Multiple servers cannot effectively share the same storage resources at
the block I/O level.
Although RAID controllers protect against drive failure, the server itself
contains many points of failure, including both hardware and software
Storage must be located very close to the host, limiting the flexibility in
the layout of the datacenter.
Because data is dispersed across dozens or hundreds of servers,
monitoring and allocating storage resources can be a complex and time-