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10. RAIT (Redundant Arrays of Inexpensive Tape)

(6/93) There are several tape array products on the market:

Data General is selling the CLARiiON Tape Array Subsystem comprising between five and seven 4mm DAT tape drives. Data can be recorded in RAID-like striping redundancy, mirrored, or in conventional DAT layout. This unit can provide up to 30GB of unattended contiguous storage. The tape drives can record at sustained rates of 183 - 732 KB/second each but customers should expect sustained backup at around 1 megabyte/second of compressed data after accounting for host overheads. Data General is working on a seven tape caddie to hold tape sets together. It is essential that tapes in a RAID group not be separated.

NCR announced a tape array software product for NCR uniprocessors and System 3450, System 3550 and StarServer Systems running UNIX V R4.2.01. This tape array software yields faster and more reliable backup of large database and file servers than with any single tape drive available today but uses customers existing tape devices. It writes simultaneously to multiple drives and can use array techniques to recover from loss or failure in any single tape.

The motivations for tape arrays seems to parallel those for disk arrays:

  • higher bandwidths
  • increased reliability

    (dwilmot@crl.com, Dick Wilmot, Editor, Independent RAID Report)

    (6/93) Pick up any DEC related trade rags and you can find an ad for an 8mm tape array. The ad I just found is by Contemporary Cybernetics and uses two five GB 8mm drives with compression - they CLAIM to be able to get 50 GB os storage total - but how many customers have 50 GB worth of 5:1 compressible data?

    Anyway - the ad doesn't mention RAID, but they support RAIDish (!) features such as striping and mirroring. It also supports offline tape-to-tape copy and will automatically cascade onto the second tape when the first one fills (useful for utilities that can't deal with multi-drive/multi- volume).

    I SEEM to remember someone having something like this with more drives, but of course I couldn't locate the ad.

    I would be really interested in seeing something like this for 3480 since the transfer rate is already quite high...

    (tbodoh@resdgs1.er.usgs.gov, Tom Bodoh)

    At the Monterey IEEE Mass Storage Conference in April '93, Ann Drapeau from Randy Katz's group presented a paper on striped tape.

    The National Storage Lab High Performance Storage System reportedly supports striping of removable media in the system software.

    (rdv,95/1/13)

    Something that came through the newsgroup recently (95/2/5):

    
    Tape Arrays
    High Performance tape drive units for large networks and minis.
    Fast: up to 4Megabyes/second
    High Capacity: from 24Gb on 4mm DATS to 60GB on DLTs; with 
    autoloaders,up to 616GB
    Flexibility: Stripe data across 4 drives, mirror data, 
    stripe 2/mirror 2 - double your speed while creating an off-site
    storage copy; off-line copy; pass-thru mode, etc.  
    Transparent to your backup software - no changes or retraining
    Compatible with all major OSs; including Novell, WindowsNT,
    Unix, Sun, HP, Silicon Graphics, VMS, etc.
    For More information:
    William Wirth
    Travlnmn@ix.net.com
    
    

    Just spotted this in a PC rag. Andataco can stripe, mirror or RAID DLT, 8mm or 4mm. Check out www.andataco.com or call 800-334-9191 or +1-619-453-9191. Or email inquire@andataco.com. (Andataco is an integrator for numerous storage products including RAID arrays.)

    Compaq now has a DLT tape array. Some specs available at www.compaq.com. Stripes or does RAID 5. (rdv, 96/4/17)

    Tecmar makes a tape array with up to 30 (custom) drives. A "rotating" spare is used to gradually back up the entire system. (Georg Feil, http://www.sgl.ists.ca/~georg, georg@sgl.ists.ca, 96/10/17)


    10.1. DataVast (was VastNSS)

    Originally developed at our institute for use in radio astronomy, the DataVast is now being built and marketed by DataVation.

    DataVast is an SVHS tape array with up to 30 tape transports and a capacity of 50 GBytes uncompressed per tape (1.5 TB total with 30 transports). DataVast is best suited for near-line networked applications. It sits on an Ethernet network and acts as an NFS file server. An internal 4 GB disk serves as a cache for recently accessed files. Except for the fact that files often take longer to access, the system appears exactly like an extremely large disk.

    File "seek" times depend on user access patterns and file sizes, but most users can expect average access times under 1 minute and worst-case access times under 3 minutes. Data transfer rates are comparable with typical Ethernet NFS servers.

    DataVast is not redundant in the sense of a RAID -- the array architecture is used to increase capacity and reduce cost (the main electronics is replicated only once for up to 30 tape transports, unlike SCSI RAIT systems where each tape drive duplicates all electronics). There is no robotics.

    See www.datavation.com.

    VastNSS is Vast Network Storage Server. This was known as VastNSS, owned by Legacy, but some of the guys split and bought the technology and founded Datavation, and renamed the product DataVast. (rdv, 97/3/18) (info updated courtesy of Michael Mansell, mansell@cimtegration.com, 97/3/18)


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    Copyright 1996 Rod Van Meter