Linked by Amjith Ramanujam on Tue 19th Aug 2008 14:44 UTC, submitted by M-Saunders
How does OpenSolaris, Sun's effort to free its big-iron OS, fare from a Linux user's point of view? Is it merely a passable curiosity right now, or is it truly worth installing? Linux Format takes OpenSolaris for a test drive, examining the similarities and differences to a typical Linux distro.
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Member since:2005-07-11
"But you as you say, you can not add a drive to an EXISTING zpool. Instead you can exchange the drives to larger ones. Yes.
A zpool can be extended with vdevs as you like. vdevs can be single drives, RAID-Z arrays, mirrors, files or LUNs. The redundancy is defined by the vdev. Put a single drive vdev in a pool and you're playing with fire. You can turn single drive vdevs into mirrors, tho. "
So, how would one take a 24-drive bay system, put 12 drives in it, configure a zpool, use the system, later add 12-drives to it, and add those to the pool?
Would you create a 12-drive raidz2 pool (say storage0), then add that to another pool (say bigstorage), then later create a second 12-drive raidz2 pool (say storage1), and then add that as a vdev to bigstorage?? Which would give you:
bigstorage
storage0
drive0
drive1
...
drive11
storage1
drive0
drive1
...
drive11
If so, that's kind of neat, but a lot of extra overhead. Although I guess it does offer a bit more redundancy (can lose up to 4 drives across the two raidz arrays).
I guess the whole vdev thing is tripping me up, as I'm thinking in terms of drives and single pools per storage server.
Edited 2008-08-20 15:17 UTC
Member since:2006-03-20
Yep, like this. Though you don't get to label vdevs.
Yet, I guess. When they finally implement vdev removal, you need to be able to address them.
--edit:
It'd work like this to create a pool with one RAID-Z array:
zpool create pacman raidz disk1 disk2 disk3 disk4
Then later, adding a second RAID-Z:
zpool add pacman raidz disk5 disk6 disk7 disk8
The end result are two RAID-Z vdevs. ZFS will then dynamically spread blocks based on parameters like write throughput and bandwidth usage.
Edited 2008-08-20 15:28 UTC
Member since:
2006-03-20
A zpool can be extended with vdevs as you like. vdevs can be single drives, RAID-Z arrays, mirrors, files or LUNs. The redundancy is defined by the vdev. Put a single drive vdev in a pool and you're playing with fire. You can turn single drive vdevs into mirrors, tho.
What you can't do is expand an existing RAID-Z vdev with more disks, you'd have to add a whole new RAID-Z vdev. The way it works to avoid the write hole makes expanding it a pain in the ass. The developers threw a lot of ideas out how this could be implemented, but it's a total non-priority for them and are encouraging third parties to give it a try if it's a priority. You can increase the size of an array tho by successively replacing each disk with a larger one.
Since ZFS is still evolving, their focus points more towards enterprise, where whole arrays are added to a storage pool to extend it, instead of expanding a single array (which is a dangerous operation).
For that matter, there's still work on implementing, testing and stabilizing some functionality (bp_rewrite) needed to perform the necessary operations safely.
Edited 2008-08-20 12:33 UTC