On Wed, Jan 20, 2010 at 2:52 PM, David Magda <dma...@ee.ryerson.ca> wrote:
>
> On Jan 20, 2010, at 12:21, Robert Milkowski wrote:
>
>> On 20/01/2010 16:22, Julian Regel wrote:
>>>
>> [...]
>>>
>>> So you could provision a tape backup for just under £30000 (~$49000). In
>>> comparison, the cost of one X4540 with ~ 36TB usable storage is UK list
>>> price £30900. I've not factored in backup software since you could use an
>>> open source solution such as Amanda or Bacula.
>>
>> [...]
>> You would also need to add at least one server to your library with fc
>> cards.
>> Then with most software you would need more tapes due to data
>> fragmentation and a need to do regular full backups (with zfs+rsync you only
>> do a full backup once).
>>
>> So in best case a library will cost about the same as disk based solution
>> but generally will be less flexible, etc. If you would add any enterprise
>> software on top of it (Legato, NetBackup, ...) then the price would change
>> dramaticallly. Additionally with ZFS one could start using deduplication (in
>> testing already).
>
> Regardless of the economics of tape, nowadays you generally need to go to
> disk first because trying to stream at 120 MB/s (LTO-4) really isn't
> practical over the network, directly from the client.
I remember for about 5 years ago (before LT0-4 days) that streaming
tape drives would go to great lengths to ensure that the drive kept
streaming - because it took so much time to stop, backup and stream
again. And one way the drive firmware accomplished that was to write
blocks of zeros when there was no data available. This also occurred
when the backup source was sending a bunch of small files, which took
longer to stream and did'nt produce enough data to keep the drive
writing useful data. And if you had the tape hardware setup to do
compression, then, assuming a normal 2:1 compression ratio, you'd need
to source 240Mb/Sec in order to keep the tape writing 120Mb/Sec. The
net result was the consumption of a lot more tape than a
back-of-the-napkin calculation told you was required.
Obviously at higher compression ratios or with the higher stream data
write rates you quote below - this problem becomes more troublesome.
So I agree with your conclusion: "The only way to realistically feed
that is from disk."
> So in the end you'll be starting with disk (either DAS or VTL or whatever),
> and generally going to tape if you need to keep stuff that's older than
> (say) 3-6 months. Tape also doesn't rotate while it's sitting there, so if
> it's going to be sitting around for a while (e.g., seven years) better to
> use tape than something that sucks up power.
>
> LTO-5 is expected to be released RSN, with a native capacity of 1.6 TB and
> (uncompressed) writes at 180 MB/s. The only way to realistically feed that
> is from disk.
>
> _______________________________________________
Regards,
--
Al Hopper Logical Approach Inc,Plano,TX a...@logical-approach.com
Voice: 972.379.2133 Timezone: US CDT
OpenSolaris Governing Board (OGB) Member - Apr 2005 to Mar 2007
http://www.opensolaris.org/os/community/ogb/ogb_2005-2007/
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