Scott Lovenberg wrote:
> First Post!
> Sorry, I had to get that out of the way to break the ice...
Welcome!
> I was wondering if it makes sense to zone ZFS pools by disk slice, and if it
> makes a difference with RAIDZ. As I'm sure we're all aware, the end of a
> drive is half as fast as the beginning ([i]where the zoning stipulates that
> the physical outside is the beginning and going towards the spindle increases
> hex value[/i]).
IMHO, it makes sense to short-stroke if you are looking for the
best performance. But raidz (or RAID-5) will not give you the
best performance. You'd be better off mirroring for performance.
> I usually short stroke my drives so that the variable files on the operating
> system drive are at the beginning, page in center (so if I'm already in
> thrashing I'm at most 1/2 a platters width from page), and static files are
> towards the end. So, applying this methodology to ZFS, I partition a drive
> into 4 equal-sized quarters, and do this to 4 drives (each on a separate SATA
> channel), and then create 4 pools which hold each 'ring' of the drives. Will
> I then have 4 RAIDZ pools, which I can mount according to speed needs? For
> instance, I always put (in Linux... I'm new to Solaris) '/export/archive' all
> the way on the slow tracks since I don't read or write to it often and it is
> almost never accessed at the same time as anything else that would force long
> strokes.
>
> Ideally, I'd like to do a straight ZFS on the archive track. I move data to
> archive in chunks, 4 gigs at a time - when I roll it in I burn 2 DVDs, 1 gets
> cataloged locally and the other offsite, so if I lose the data, I don't care
> - but, ZFS gives me the ability to snapshot to archive (I assume it works
> across pools?). Then stripe 1 ring (I guess this is ZFS native?),
> /usr/local (or its Solaris equivalent) for performance. Then mirror the root
> slice. Finally, /export would be RAIDZ or RAIDZ2 on the fastest track,
> holding my source code, large files, and things I want to stream over the LAN.
>
> Does this make sense with ZFS? Is the spindle count more of a factor than
> stroke latency? Does ZFS balance these things out on its own via random
> scattering?
Spindle count almost always wins for performance.
Note: bandwidth usually isn't the source of perceived performance
problems, latency is. We believe that this has implications for
ZFS over time due to COW, but nobody has characterized this yet.
> Reading back over this post, I've found it sounds like the ramblings of a
> madman. I guess I know what I want to say, but I'm not sure the right
> questions to ask. I think I'm saying: Will my proposed setup afford me the
> flexibility to zone for performance since I have a more intimate knowledge of
> the data going onto the drive, or will brute force by spindle count (I'm
> planning 4-6 drives - single drive to a bus) and random placement be
> sufficient if I just add the whole drive to a single pool?
Yes :-) YMMV.
> I thank you all for your time and patience as I stumble through this, and I
> welcome any point of view or insights (especially those from experience!)
> that might help me decide how to configure my storage server.
KISS.
There are trade-offs for space, performance, and RAS. We have models
to describe these, so you might check out my blogs on the subject.
http://blogs.sun.com/relling
-- richard
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