[ILUG] Cheap tape drives
paul at clubi.ie
Mon Mar 18 17:21:20 GMT 2002
On Mon, 18 Mar 2002, Wynne, Conor wrote:
> Because you've got both!
ah.. of course. :)
> You got RAID sets with online spares, and then you got you three
> backups -> verified with restore jobs and kept in cold storage
> offsite, along with hardcopies of everything too. [This is for
> <SMALL> company]
hardcopies of everything? eek.
> DAT : Needs regular cleaning, and the cleaning tapes must be
> changed regularly to boot. Cheap drives and media. 2 heads in
> cartridge and your data layer gets pulled over the heads, which
> wears out the tapes.
worse, DAT uses helical scan heads (ala VCRs), ie the head is offset
wrt to the direction of the tape travel and spins, ie:
------> tape \ head
quite abrasive on the tapes.
DAT, imo, is not reliable.
DLT is very nice though. but /very/ expensive. And seeing as how the
main argument for backing up to IDE disks is cost, we can assume
we're talking about a scenario where the cost of DLT is a big
> If you have a big company then you add a storage area network, with
> entire boxes full of drives, with fibre interconnects and mirror
> sans, snapshotting over dark fibre links, whats that 75KM between
> nodes or so in case of disaster? 10/11 anyone?
go ask Eircom for a couple of Km's of fibre... :)
> hear stories of people that say, make a raid1, remove a drive and
> stick it somewhere "safe", replace the drive and let her rebuild,
> then it all dies, they add the old raid1 disk and its doesn't
> rebuild for some reason, there can be many reasons why this may be,
> one example is the drive they thought was blank had in actual fact,
> been used as a previous raidset. Both drives think thay should
> rebuild over the other... kaboom! You mount it and you see old
> rubbish instead of your mission critical data.
cant say i have heard of that, if i knew of a controller that was
that silly i'd be sure to avoid that make for ever more¹.
you're biased here cause you work in compaq support and are exposed
only to about 3 sets of RAID controllers (ttbomk: the old 2 series,
the on-board "controller" that replaced it at low-end, the 3200 and
4200 boards that replaced the 2 series at the mid and high end). and
obviously you're over-exposed to any bugs these might have wrt to
rebuilding drive sets.
anyway, if we're looking at cost to come up with reliable and cheap
backup solution, then a RAID controller would not be involved, would
it? you'd just use linux md mirroring.
wrt to "you hear of people doing backups, putting the xxxx away to a
safe place, then when they need to restore from it, they just get
rubbish", ime xxxx would typically == DAT. :)
> Lastly, disks don't move well at all. Try shaking one :)
laptops seem to get on grand...
> I think a good setup [for the uncle] will be RAID 1 for system,
> RAID5 or maybe raid 0+1 for the paranoid. DAT or maybe AIT aswell
> as CDbackups [CDR not CDRW]. Its a very small office.
but he's got 100G+ of data to backup.. (he's got a little server with
3 50G IDE disks, and his new desktop PC came with a 70GB disk)
with DAT he's going to have spend significant amount of time each
evening or morning changing tapes.
DLT he cant really afford. he could afford a few more IDE disks
> Boi Boi,
> as a matter of curiosity, given that disk drives have seen such
> spectacular increase in capacity, and you could probably buy 3 or 4
> 50GB+ IDE drives for the cost of a low-end (and low GB) tape
> solution, why not just buy lots of disks and a hot swap / removable
> caddy IDE drive cage?
> (eg DAT DDS4 + 10ish 12GB tapes is maybe £400. you could buy easily
> buy 2 big IDE disks + caddies/cage for that money. make redundant
> backups to the disks, you're still ahead of the tapes.)
> and DAT isnt exactly ultra reliable either and DLT costs loads of
Paul Jakma paul at clubi.ie paul at jakma.org Key ID: 64A2FF6A
In Boston, it is illegal to hold frog-jumping contests in nightclubs.
1. mylex's are quite cute in this regard: the array configuration is
held on disk and in nvram (same as with the compaq controllers, and i
guess most half-decent controllers). however, with the mylex you can
make copies of the configuration to a floppy. so if you're doing
something tricky you just make a backup with each change, and so if
it goes wrong and you've buggered the on-drive and nvram config data,
you can just restore from the floppy... saved my arse a few times.
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