Depends on your performance needs, future scalability and tolerance for failure.
a - I assume you mean striped mirrors.
best performance
easy to expand (just add 2 more drives)
if you lose 2 drive in the same mirro, pool is toast.
b - for the super paranoid, who don't want to have to worry about a physical failure
c - for the super paranoid, who don't want to worry about a physical failure, but don't realize that having a hot spare sitting there is just as likely to fail as if it were part of a RAID-Z3 (which is where it would be better utilized.
Depending on how much usable space you want, the best utilization/performance tradeoff, if it were my pool, would be a 6 Drive RAID Z2, with a cold spare sitting on a shelf. If you didn't have close access to the machine (and maybe couldn't quickly replace a failed drive), then RAID-Z3.
I assume you are thinking of the n^2 + y "rule" (where n is the number of "data disks" and y is the number of "parity disks" -- OK, I know that's not how RaidZ works, but I can't think of a better way to put it); but I've read on these forums that this "rule" no longer applies -- for reasons that I no longer recall.
And doesn't the first of your preferred configurations (6-drive RAIDZ2 + cold spare) have the same disadvantage as my (b) suggestion? Wouldn't that spare 7th drive be better employed as part of a 7-drive RAIDZ3 pool? -- and not just "If you didn't have close access to the machine (and maybe couldn't quickly replace a failed drive)"?
Maybe I assumed wrongly that it is possible.I didn't know you could configure mirrored stripes in the GUI. cool!
That's good, but whether I'll use it is another story.Hot spare functionality was recently added.
No: I specified 6 drives because that's the number of 6TB Seagates I picked up today at BestBuy for $61.99 apiece.The difference between 6 Drive RAID Z2 and 6 Drive RAID-Z3, is the loss of one more drives worth of space. If space isnt important, then they are at the same disadvantage level.
Yes it would be better employed as a 7th disk in a RAID-Z3, but I was under the impression your system could only handle 6 drives.:)
But a hot spare can still be having regular SMART tests. A cold spare might be found to be useless when it's powered up.It's due to compression being the default now. The rule doesn't apply for performance but seems to still apply for overhead reduction. However I'm not 100% sure because I've not talked (yet) to some devs. And even if it's true it's a very small overhead; in short, don't worry and put the number of drives you want ;)
No because it's a cold spare, so the drive isn't wearing out doing nothing like with a hot spare.
NB: a RAID-Z3 with 6 drives is very paranoid (and mirrored 3 drives stripes are the opposite...), far more than what I am, why you want this very high redundancy?
That's because you can't. It can't be done with ZFS.I didn't know you could configure mirrored stripes in the GUI. cool!
A cold spare might be found to be useless when it's powered up.
And I was about to ask: someone -- perhaps you -- posted a script that executes an extensive test of one or more drives, but I can't find it. Was it yours, or do you know where I could find it? I don't think it just runs SMART conveyance and long tests.That's why you need to burn it in before putting it on the shelf as a spare ;)
Found it. Thanks.It was jgreco :)
I think it's in the burn in hardware thread, do a search and use jgreco in the member field, you should find it easily that way ;)
That's because you can't. It can't be done with ZFS.
I was talking about a mirror of stripes rather than a stripe of mirrors, and it's the former that Ericloewe says can't be done.Oracles documentation on ZFS disagrees with this:
Storage Configuration
We recommend that a mirrored (RAID10) configuration be used for Oracle VDI deployments to meet the demanding random I/O patterns produced by a large number of virtual desktops accessing the same physical disk spindles. Mirrored disk pools are able to provide the needed IOPs at low latency, which prevents desktop users from experiencing desktop lag or slowness. Parity disk pools (either single- or double-parity RAID) may provide acceptable performance in low usage or demonstration configurations, but care should be taken to perform a detailed pre-deployment test validation to confirm that such a pool layout is adequate to meet user needs before the system is put into production.
RAID10 - a stripe of mirrors
Oracles documentation on ZFS disagrees with this:
Storage Configuration
We recommend that a mirrored (RAID10) configuration be used for Oracle VDI deployments to meet the demanding random I/O patterns produced by a large number of virtual desktops accessing the same physical disk spindles. Mirrored disk pools are able to provide the needed IOPs at low latency, which prevents desktop users from experiencing desktop lag or slowness. Parity disk pools (either single- or double-parity RAID) may provide acceptable performance in low usage or demonstration configurations, but care should be taken to perform a detailed pre-deployment test validation to confirm that such a pool layout is adequate to meet user needs before the system is put into production.
RAID10 - a stripe of mirrors