Computer data storage - Some glossary
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|Computer data storage|
|This article/section is a stub — probably a pile of half-sorted notes and is probably a first version, is not well-checked, so may have incorrect bits. (Feel free to ignore, or tell me)|
DAS (Direct Attached Storage) - storage not physically in a host, but still connected directly to just it
- often means a connection like SAS, SCSI, Fibre Channel, eSATA or such (various are easily be faster than networking)
SAN (Storage Area Network)
- often exposes a block device(verify)
- often there to centralized a large amount of storage for a network of computers.
- you arguably do SAN for consolidation and flexibility first, and performance may be secondary
- e.g. iSCSI is a SAN protocol
NAS (Network Attached Storage) - Storage attached via a (local area) network.
- Can refer to simple file sharing (SMB, NFS and such), to specific applicances.
- often exposes a filesystem
- more of an appliance (SAN being more of a service)
- S.M.A.R.T.: Self-Monitoring Analysis and Report Technology, meant to monitor drive health and warn about imminent failure.
- (Compliance with this standard possibly seems to vary per manufacturer, and also probably somewhat per drive design)(verify)
- see also Computer data storage - Reading SMART reports
- Command queueing refers to planning an order of read and/or write commands order so that head position and rotational position are taken into account.
- In the best case a series of operations finishes faster, in the worst case it makes no difference and the overhead (fairly little for NCQ, while for TCQ it depends somewhat on the implementation/technology) makes things a little slower. The practical value of command queueing depends largely on the average and worst case influence.
- TCQ: Tagged Command Queueing: Done by the driver (verify)
- NCQ: Native Command Queueing: Done by the drive (SATA feature, optional?(verify)).