ZFS-inly server and dedicated ZIL

[Dmitry Morozovsky]

On Wed, 10 Apr 2013, Lawrence K. Chen, P.Eng. wrote:

> The root pool only having one root vdev is probably a restriction on what functionality could be put into the bootblock.
> 
> But, can't really tell what it is you're trying to do...
> 
> You say raid10-like ZFS with two SSDs....which to me means you have at least 4 physical drives, and 2 SSDs.
> 
> zpool create tank mirror disk1 disk2 mirror disk3 disk4 .... log ... cache ....
> 
> perhaps as: .... log mirror ssd1a ssd2a cache ssd1b ssd2b

Yes, exactly this way (gpt partitions, but nevermind). And before adding log I 
booted from this pool perfectly.

> tank is load-balancing onto sets of mirrors, with a mirror of the first 
> partition of the two ssds for ZIL and using the second partition of the two 
> ssds concurrently for cache.
> 
> So, in this case....tank can't be used as a root pool.  an Internal USB stick 
> as your root pool would be one way to go.  or you could carve out another 
> partition on the SSDs for a root pool.

I'm now thinking of putting /boot on the first pair of disks to boot from, 
avoiding SPOF in this area too.


> On my home system, I currently have a pair of SSDs....each with 7 
> partitions.... 5 tiny ones for mirror ZILs for the other zpools in my system, 
> the mirrored root pool and partitions to be L2ARC for the two zpools in my 
> system that I'm using dedup in.  (there's currently only 4 zpools in my 
> system, including the root....but I had originally envisioned the possibility 
> of adding additional external jbod arrays....)

What is not clear for me is why one could want more than one pool in one 
machine?

Thanks for your comments, will test further.


> 
> I used to have 6 disk raid10-like with part of an external SSD for its zil...and no cache.  It has since been redone as a raidz2 with mirrored zil (from the internal SSDs)....planning to add another SSD soon.
> 
> ----- Original Message -----
> > Dear colleagues,
> > 
> > I'm planning to make new PostgreSQL server using zaid10-like ZFS with
> > two SSDs
> > splitted into mirrored ZIL and striped arc2. However, it seems
> > current
> > ZFS implementation does not support this:
> > 
> > ./lib/libzfs/common/libzfs_pool.c-		case EDOM:
> > ./lib/libzfs/common/libzfs_pool.c-			zfs_error_aux(hdl,
> > dgettext(TEXT_DOMAIN,
> > ./lib/libzfs/common/libzfs_pool.c:			    "root pool can not have
> > multiple vdevs"
> > ./lib/libzfs/common/libzfs_pool.c-			    " or separate logs"));
> > ./lib/libzfs/common/libzfs_pool.c-			(void) zfs_error(hdl,
> > EZFS_POOL_NOTSUP, msg);
> > 
> > Am I right, or did I missed something obvious?
> > 
> > Ok, if so: In this situation, I see two possibilities:
> > - make system boot from internal USB stick (only /bootdisk with /boot
> > and
> > /rescue) with the rest of ZFS-on-root
> > - use dedicated pair of disks for ZFS pool without ZIL for system.
> > 
> > what would you recommend?
> > 
> > Thanks!
> > 
> > --
> > Sincerely,
> > D.Marck                                     [DM5020, MCK-RIPE,
> > DM3-RIPN]
> > [ FreeBSD committer:
> >                                 marck at FreeBSD.org ]
> > ------------------------------------------------------------------------
> > *** Dmitry Morozovsky --- D.Marck --- Wild Woozle --- marck at rinet.ru
> > ***
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-- 
Sincerely,
D.Marck                                     [DM5020, MCK-RIPE, DM3-RIPN]
[ FreeBSD committer:                                 marck at FreeBSD.org ]
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*** Dmitry Morozovsky --- D.Marck --- Wild Woozle --- marck at rinet.ru ***
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