On 01/20/2018 04:07 AM, Jim Wiggs 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.
You don't need mirrors, so you could have used a small write intensive SSD for your log and a bigger general purpose one for your cache.
For KVM workloads on SmartOS, you are better of spending your money on the best log device(s) you can afford and skip the cache. Spend the money on more RAM! I haven't looked recently but Joyent's recommended system builds didn't have cache devices.
Cheers, Ian. ------------------------------------------- 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
