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/184463/29487083-1299c373> | > Modify > <https://www.listbox.com/member/?&;> > Your Subscription <http://www.listbox.com> > ------------------------------------------- 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
