On Mar 16, 2013, at 7:01 PM, Andrew Werchowiecki <andrew.werchowie...@xpanse.com.au> wrote:
> It's a home set up, the performance penalty from splitting the cache devices > is non-existant, and that work around sounds like some pretty crazy amount of > overhead where I could instead just have a mirrored slog. > > I'm less concerned about wasted space, more concerned about amount of SAS > ports I have available. > > I understand that p0 refers to the whole disk... in the logs I pasted in I'm > not attempting to mount p0. I'm trying to work out why I'm getting an error > attempting to mount p2, after p1 has successfully mounted. Further, this has > been done before on other systems in the same hardware configuration in the > exact same fashion, and I've gone over the steps trying to make sure I > haven't missed something but can't see a fault. You can have only one Solaris partition at a time. Ian already shared the answer, "Create one 100% Solaris partition and then use format to create two slices." -- richard > > I'm not keen on using Solaris slices because I don't have an understanding of > what that does to the pool's OS interoperability. > ________________________________________ > From: Edward Ned Harvey (opensolarisisdeadlongliveopensolaris) > [opensolarisisdeadlongliveopensola...@nedharvey.com] > Sent: Friday, 15 March 2013 8:44 PM > To: Andrew Werchowiecki; zfs-discuss@opensolaris.org > Subject: RE: partioned cache devices > >> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- >> boun...@opensolaris.org] On Behalf Of Andrew Werchowiecki >> >> muslimwookie@Pyzee:~$ sudo zpool add aggr0 cache c25t10d1p2 >> Password: >> cannot open '/dev/dsk/c25t10d1p2': I/O error >> muslimwookie@Pyzee:~$ >> >> I have two SSDs in the system, I've created an 8gb partition on each drive >> for >> use as a mirrored write cache. I also have the remainder of the drive >> partitioned for use as the read only cache. However, when attempting to add >> it I get the error above. > > Sounds like you're probably running into confusion about how to partition the > drive. If you create fdisk partitions, they will be accessible as p0, p1, > p2, but I think p0 unconditionally refers to the whole drive, so the first > partition is p1, and the second is p2. > > If you create one big solaris fdisk parititon and then slice it via > "partition" where s2 is typically the encompassing slice, and people usually > use s1 and s2 and s6 for actual slices, then they will be accessible via s1, > s2, s6 > > Generally speaking, it's unadvisable to split the slog/cache devices anyway. > Because: > > If you're splitting it, evidently you're focusing on the wasted space. > Buying an expensive 128G device where you couldn't possibly ever use more > than 4G or 8G in the slog. But that's not what you should be focusing on. > You should be focusing on the speed (that's why you bought it in the first > place.) The slog is write-only, and the cache is a mixture of read/write, > where it should be hopefully doing more reads than writes. But regardless of > your actual success with the cache device, your cache device will be busy > most of the time, and competing against the slog. > > You have a mirror, you say. You should probably drop both the cache & log. > Use one whole device for the cache, use one whole device for the log. The > only risk you'll run is: > > Since a slog is write-only (except during mount, typically at boot) it's > possible to have a failure mode where you think you're writing to the log, > but the first time you go back and read, you discover an error, and discover > the device has gone bad. In other words, without ever doing any reads, you > might not notice when/if the device goes bad. Fortunately, there's an easy > workaround. You could periodically (say, once a month) script the removal of > your log device, create a junk pool, write a bunch of data to it, scrub it > (thus verifying it was written correctly) and in the absence of any scrub > errors, destroy the junk pool and re-add the device as a slog to the main > pool. > > I've never heard of anyone actually being that paranoid, and I've never heard > of anyone actually experiencing the aforementioned possible undetected device > failure mode. So this is all mostly theoretical. > > Mirroring the slog device really isn't necessary in the modern age. > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss -- ZFS and performance consulting http://www.RichardElling.com _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
