Chris Cosby wrote:
I'm going down a bit of a different path with my reply here. I know that all
shops and their need for data are different, but hear me out.
1) You're backing up 40TB+ of data, increasing at 20-25% per year. That's
insane. Perhaps it's time to look at your backup strategy no from a hardware
perspective, but from a data retention perspective. Do you really need that
much data backed up? There has to be some way to get the volume down. If
not, you're at 100TB in just slightly over 4 years (assuming the 25% growth
factor). If your data is critical, my recommendation is to go find another
job and let someone else have that headache.
Well, we are talking about backup for ~900 servers that are in
production. Our retention period is 14 days for stuff like web servers,
and 3 weeks for SQL and such.
We could deploy deduplication but it makes me a wee bit uncomfortable to
blindly trust our backup software.
2) 40TB of backups is, at the best possible price, 50-1TB drives (for spares
and such) - $12,500 for raw drive hardware. Enclosures add some money, as do
cables and such. For mirroring, 90-1TB drives is $22,500 for the raw drives.
In my world, I know yours is different, but the difference in a $100,000
solution and a $75,000 solution is pretty negligible. The short description
here: you can afford to do mirrors. Really, you can. Any of the parity
solutions out there, I don't care what your strategy, is going to cause you
more trouble than you're ready to deal with.
Good point. I'll take that into consideration.
I know these aren't solutions for you, it's just the stuff that was in my
head. The best possible solution, if you really need this kind of volume, is
to create something that never has to resilver. Use some nifty combination
of hardware and ZFS, like a couple of somethings that has 20TB per container
exported as a single volume, mirror those with ZFS for its end-to-end
checksumming and ease of management.
That's my considerably more than $0.02
On Thu, Jul 3, 2008 at 11:56 AM, Bob Friesenhahn
[EMAIL PROTECTED] wrote:
On Thu, 3 Jul 2008, Don Enrique wrote:
This means that i potentially could loose 40TB+ of data if three
disks within the same RAIDZ-2 vdev should die before the resilvering
of at least one disk is complete. Since most disks will be filled i
do expect rather long resilvering times.
Yes, this risk always exists. The probability of three disks
independently dying during the resilver is exceedingly low. The chance
that your facility will be hit by an airplane during resilver is
likely higher. However, it is true that RAIDZ-2 does not offer the
same ease of control over physical redundancy that mirroring does.
If you were to use 10 independent chassis and split the RAIDZ-2
uniformly across the chassis then the probability of a similar
calamity impacting the same drives is driven by rack or facility-wide
factors (e.g. building burning down) rather than shelf factors.
However, if you had 10 RAID arrays mounted in the same rack and the
rack falls over on its side during resilver then hope is still lost.
I am not seeing any options for you here. ZFS RAIDZ-2 is about as
good as it gets and if you want everything in one huge pool, there
will be more risk. Perhaps there is a virtual filesystem layer which
can be used on top of ZFS which emulates a larger filesystem but
refuses to split files across pools.
In the future it would be useful for ZFS to provide the option to not
load-share across huge VDEVs and use VDEV-level space allocators.
Bob
==
Bob Friesenhahn
[EMAIL PROTECTED], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,http://www.GraphicsMagick.org/
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Henrik Johansen
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