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, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)


DAS (Direct Attached Storage) - storage not physically in a host, but connected directly to just it (via SAS, SCSI, Fibre Channel, eSATA or such), May easily be faster than networking.

NAS (Network Attached Storage) - Storage attached via a (local area) network. Can refer to simple file sharing (SMB, NFS and such), to specific applicances.

SAN (Storage Area Network) - similar to NAS, but more specifically geared to be a centralized, dedicated storage service for a network of computers. (More of a service, while NAS is more of an appliance). SAN implementations often refer to larger-scale consolidated things.

iSCSI - effectively one implementation of NAS (and arguably SAN), with the largest difference being that it looks like a block device rather than a remote share.


  • 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)).