On Fri, Jan 19, 2018 at 7:49 AM, Sam Nicholson <[email protected]> wrote:
> I'll throw my $.02 behind you Jim. Perhaps splitting an SSD is not the > best way to get the most performance out of the SSD. > But even a part of an SSD is a huge win. In fact, separate logs have > always been a win, even back in the pre-ZFS days. I > recall some old Bonnie results from the late '90 that show separating logs > onto partitions *on the same drive* is a good deal. > Relative to the bare drive performance, that is. Not relative to optimal > combinations of fast 2.5 inch 15K SAS for logs. > > My standard is to use 2 SSDs and 2 HDDs. Mirror the HDDs for reliability, > split the SSD into a small slice for a mirrored log, > and a spanned cache. Remember, there is no need to mirror the cache. > Errors there are treated just like misses, they are > read from primary volume. > > It looks like this: > > *# zpool create zones mirror c0t0d0 c0t1d0 log mirror c0t2d0s4 c0t3d0s4 > cache c0t2d0s5 c0t3d0s5* > > Having used format(1m) to partition c0t2 and c0t3 with Solaris labels with > partitions 4 and 5 as the LOG and CACHE parts, respectively. > Size of part 4 depends upon your write speed. Max write rate * 5 seconds > rounded up. I use 8 GB logs for my 10G connected NFS server. > 10 Gbits * 5 (rounded up to 56) / 8bits = 7, which I round up to 8 > GBytes. The rest is cache. > > It's *so* much better than just the mirrored HDD. But I do see contention > for the SSD under heavy load. So What!? > My HDDs would have melted by now. > > Only caveat is that TRIM support may be affected. I don't know, I haven't > looked into the behavior. That's a good Q for another topic. > > As to Parted being not there. I'd gently advise to use native tools. > format(1m) has fdisk, partition, and label within. > I'm going to be rebuilding a couple of servers later today. I'll capture > the format session I use and send it to you, if you like. > I use Parted(8) on Linux. I don't like it, but I use it. :) > > Cheer! > -sam > > On Fri, Jan 19, 2018 at 10:07 AM, Jim Wiggs <[email protected]> wrote: > >> I've been told by quite a few folks that splitting the SSD between log >> and cache is "a bad idea" or "suboptimal" but frankly, I don't buy it. It >> may just be my personal experience, but for my use cases, I've been >> operating with limited resources and haven't been able to justify the >> expense of having three or more SSDs to do this. Since I've never needed a >> ZIL with more than 2 GB of space and the smallest SSDs you can buy are more >> than 10x that size, mirroring a pair of SSDs for the ZIL was a huge waste >> of space. I started doing this about 4 years ago when SSDs were much more >> expensive and I couldn't justify that waste, so I'd partition a 1-2 GB >> slice on each SSD and mirror them for my ZIL, and use the remaining space >> on both SSDs, un-mirrored, for cache. Again, in my experience, this has >> always resulted in better general performance than either adding only log >> or only cache. >> >> YMMV. >> >> On Fri, Jan 19, 2018 at 1:07 AM, Ian Collins <[email protected]> >> wrote: >> >>> On 01/19/2018 08:45 PM, Jim Wiggs wrote: >>> >>>> So all is right with the world again. But I'm still left with one >>>> question: why on Earth is *parted* not included as part of the SmartOS >>>> hypervisor image? The old Solaris format command is spectacularly >>>> user-unfriendly and always has been. I can't imagine that parted requires >>>> so much additional space that it couldn't be included. Was there any >>>> particular rationale to not put a better and more user-friendly >>>> partitioning tool into the OS that runs at the top level and manages the >>>> hardware? >>>> >>>> >>> As Jussi said, partitioning disks on a ZFS only system is uncommon. >>> >>> Splitting an SSD between log and cache generally isn't a very performant >>> option. Devices that make good cache devices may not be good logs. With >>> SmartOS running KVM, there is a big gain from log devices, but not much >>> from a cache. >>> >>> Cheers, >>> Ian. >>> >> >> > *smartos-discuss* | Archives > <https://www.listbox.com/member/archive/184463/=now> > <https://www.listbox.com/member/archive/rss/184463/29472822-e06597f7> | > Modify > <https://www.listbox.com/member/?&;> > Your Subscription <http://www.listbox.com> > Thanks Sam, it's good to know there's other folks out there who see it this way. If I'd had the money to shell out to buy three or four SSDs when building a new ZFS rig, I might have gotten into that mindset, but these days whenever I hear someone say that doing what I do is a bad idea, my immediate impulse is to just say "prove it." If you've only got the money to buy a pair of SSDs and you want to get the most bang for the buck, mirroring them and using them as ZIL is *not* the way to do it. You'll be wasting 90% or more of that fast space, which will never end up being touched by the ZIL, and you'll have no fast cache to improve your reads. Sorry, but you're not going to convince me that the occasional contention between ZIL and cache on the same drives will cause a bigger performance hit than *not having the cache at all*. And yes, I'd very much like to get that format session if it's not too much trouble. My days of doing disk partitioning under Solaris are nearly 20 years in the rearview mirror, and finding a refresher on "format" on the web turned out to be much harder than I expected. best, Jim ------------------------------------------- smartos-discuss Archives: https://www.listbox.com/member/archive/184463/=now RSS Feed: https://www.listbox.com/member/archive/rss/184463/25769125-55cfbc00 Modify Your Subscription: https://www.listbox.com/member/?member_id=25769125&id_secret=25769125-7688e9fb Powered by Listbox: http://www.listbox.com
