Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!sol.ctr.columbia.edu!emory!att!cbnewsh!wcs
From: wcs@cbnewsh.att.com (Bill Stewart 908-949-0705 erebus.att.com!wcs)
Newsgroups: comp.arch
Subject: Re: Memory hierarchy
Message-ID: <1991Apr4.065126.1549@cbnewsh.att.com>
Date: 4 Apr 91 06:51:26 GMT
References: <00670398761@elgamy.RAIDERNET.COM> <-+EAGCE@xds13.ferranti.com> <3306@crdos1.crd.ge.COM>
Organization: AT&T Bell Labs Special Services Division
Lines: 36

In article <3306@crdos1.crd.ge.COM> davidsen@crdos1.crd.ge.com (bill davidsen) writes:
]   The problem is that the optical disks fall at a funny place in the
] hierarchy. Typically the ration of cache to memory, memory to disk,
] disk to tape is an order of magnitude in size, access time, and
] cost/bit. Optical is not on that path in terms of size or cost, and with
] new larger disks, neither are tapes. There is a real need for a large
] backup medium right now.

Tapes haven't been much bigger than disks for ages.  Back in 1980 or so,
my VAX had 256MB removable disk drives, and we had the expensive 6250bpi
tape which held 140MB on a good day when they were working and a huge 4MB RAM. 
Lots of people were stuck with 1600bpi tape drives, 30-40 MB.
We did incremental backups to reduce tape-changing labor as well as to
allow on-line backups when we had the space.  
Disk platters cost ~$1000, tapes $25.  Disk drives were $35K.
We could afford 4 disk drives = 1GB, which needed about 8 tapes to back up.

Today, DATs are 1 GB (2GB real soon), and slow 8mm tape is 5GB.
You can finally back up most disk drives on a single tape, and you can
get a DAT stacker holding 10 tapes.  It's a lot less annoying.
With our current reduced budgets, we can afford about 20GB of disk :-)

Removable disks now cost ~$1000-2000 for 500MB - 1GB, including the drive,
and tapes are still about $25.

]   I have faith in capitalism, there will be something better soon.
Well, if you've got the cash, you can do anything from a pair of DATs
or small stacker, which gives you a fair amount of unattended backup /recovery,
to optical disk jukebox-based systems like Epoch or AT&T's nice
CommVault 3-D File System (plug, plug), to evil monstrosities like
the 50-foot-long robotic mag-tape handler a Lawrence Livermore Labs.
-- 
				Pray for peace;		  Bill
# Bill Stewart 908-949-0705 erebus.att.com!wcs AT&T Bell Labs 4M-312 Holmdel NJ
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