On 6 Oct 2016, at 5:13, Paul B. Henson wrote: > On Thu, Oct 06, 2016 at 03:42:36AM +0100, Adam Richmond-Gordon wrote: > >> Thank you for pointing that out - I had it in my head that a single >> log device would be safe. > > There's only one failure mode (AFAIK) where a single log device will > cause data loss; if your box crashes or has an unclean shutdown (say due > to a power failure) while there are uncommitted entries on the log > device, and the device fails before the system comes back online to > process them. > > If the device dies while the system is running the log will fall back to > being on the pool and any uncommitted entries are still in memory and > won't be lost. If the device dies after a clean shutdown or poweroff > there won't be any uncommitted entries on it and when the system comes > up it will fail the device and again just fall back to an on-pool log. > > So while it's true that a single log device is non-redundant, it's a lot > less "not safe" than say a non-redundant pool. You'd have to be pretty > unlucky to actually have data loss from losing a non-redundant log > device. Of course, depending on the importance of your data, that might > not be a risk you want to take. But for a budget sensitive system, a > single high-cost SSD for a log isn't an insane configuration if you > think the odds of your system crashing/powering off dirty at the exact > same time your log device dies are pretty low.
Understood. However... In a traditional spinning rust environment with many disks, a power loss is exactly when some disks fail to come back at power on, and the failure rate increases as the system ages. While SSDs remove the mechanical element of those failures, a sudden power loss can induce electronic failures. Are there any statistics out there for SSD failure after sudden power loss? P.S. A better name for Uninterruptible Power Supplies is Less Interruptible Power Supplies. ------------------------------------------- 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
