Ok, previous threads have lead me to believe that I want to make raidz vdevs [0] either 3, 5 or 9 disks in size [1]. Let''s say I have 8 disks. Do I want to create a zfs pool with a 5-disk vdev and a 3-disk vdev? Are there performance issues with mixing differently sized raidz vdevs in a pool? If there *is* a performance hit to mix like that, would it be greater or lesser than building an 8-disk vdev? -brian [0] - Just for clarity, what are the "sub-pools" in a pool, the actual raidz/mirror/etc "containers" called. What is the correct term to refer to them? I don''t want any extra confusion here. ;) [1] - For RAID-Z. How does RAID-Z2 effect this?
On Thu, 12 Oct 2006, Brian Hechinger wrote:> Ok, previous threads have lead me to believe that I want to make raidz > vdevs [0] either 3, 5 or 9 disks in size [1]. Let''s say I have 8 disks. > Do I want to create a zfs pool with a 5-disk vdev and a 3-disk vdev?Personally I think that 5 disks for raidz is the "sweet spot". With the remaining 3 disks, consider a 3-way mirror if redundancy is more important than space. This will give you two pools with different operational characteristics.> Are there performance issues with mixing differently sized raidz vdevs > in a pool? If there *is* a performance hit to mix like that, would itCan you tell us what size your disks are?> be greater or lesser than building an 8-disk vdev?In this situation a little experimenting will probably answer all your questions. ZFS is so quick at, well, at everything, that its fun and productive to experiment with different disk configurations.> -brian > > [0] - Just for clarity, what are the "sub-pools" in a pool, the actual > raidz/mirror/etc "containers" called. What is the correct term to refer > to them? I don''t want any extra confusion here. ;) > > [1] - For RAID-Z. How does RAID-Z2 effect this?For raidz2, the corresponding #s would be 4,6 and 10 (not recommended) Al Hopper Logical Approach Inc, Plano, TX. al at logical-approach.com Voice: 972.379.2133 Fax: 972.379.2134 Timezone: US CDT OpenSolaris.Org Community Advisory Board (CAB) Member - Apr 2005 OpenSolaris Governing Board (OGB) Member - Feb 2006
On Thu, Oct 12, 2006 at 08:52:34AM -0500, Al Hopper wrote:> On Thu, 12 Oct 2006, Brian Hechinger wrote: > > > Ok, previous threads have lead me to believe that I want to make raidz > > vdevs [0] either 3, 5 or 9 disks in size [1]. Let''s say I have 8 disks. > > Do I want to create a zfs pool with a 5-disk vdev and a 3-disk vdev? > > Personally I think that 5 disks for raidz is the "sweet spot". With the > remaining 3 disks, consider a 3-way mirror if redundancy is more important > than space. This will give you two pools with different operational > characteristics.I''ll take space over redundancy in this case. :)> > Are there performance issues with mixing differently sized raidz vdevs > > in a pool? If there *is* a performance hit to mix like that, would it > > Can you tell us what size your disks are?They will be 400GB or 500GB disks.> > be greater or lesser than building an 8-disk vdev? > > In this situation a little experimenting will probably answer all your > questions. ZFS is so quick at, well, at everything, that its fun and > productive to experiment with different disk configurations.As soon as I get the disks in, I will certainly have to give them a run for their money. ;)> > [1] - For RAID-Z. How does RAID-Z2 effect this? > > For raidz2, the corresponding #s would be 4,6 and 10 (not recommended)That''s what I guessed, but wanted to make sure. Thanks!!! -brian
Brian Hechinger wrote:> Ok, previous threads have lead me to believe that I want to make raidz > vdevs [0] either 3, 5 or 9 disks in size [1]. Let''s say I have 8 disks. > Do I want to create a zfs pool with a 5-disk vdev and a 3-disk vdev? > Are there performance issues with mixing differently sized raidz vdevs > in a pool? If there *is* a performance hit to mix like that, would it > be greater or lesser than building an 8-disk vdev?Unless you are running a database (or other record-structured application), or have specific performance data for your workload that supports your choice, I wouldn''t worry about using the power-of-two-plus-parity size stripes. I''d choose between (in order of decreasing available io/s): 4x 2-way mirrors (most io/s and most read bandwidth) 2x 4-way raidz1 1x 8-way raidz1 (most write bandwidth) 1x 8-way raidz2 (most redundant)> [0] - Just for clarity, what are the "sub-pools" in a pool, the actual > raidz/mirror/etc "containers" called. What is the correct term to refer > to them? I don''t want any extra confusion here. ;)We would usually just call them "vdevs" (or to be more specific, "top-level vdevs"). --matt