Date: Mon, 06 Oct 2014 05:09:34 +0900 From: poyopoyo@puripuri.plala.or.jp To: Warren Block <wblock@wonkity.com> Cc: FreeBSD Filesystems <freebsd-fs@freebsd.org> Subject: Re: Mirrored SSDs for ZIL/SLOG - safety, flushing, capacitors Message-ID: <864mvigtxd.wl%poyopoyo@puripuri.plala.or.jp> In-Reply-To: <alpine.BSF.2.11.1410030547070.32407@wonkity.com> References: <CAP1HOmRYy8cX9k7rs4UEzx41Og4phX5U_2OpiUCKBDSRdMf_bQ@mail.gmail.com> <alpine.BSF.2.11.1410030547070.32407@wonkity.com>
next in thread | previous in thread | raw e-mail | index | archive | help
At Fri, 3 Oct 2014 05:59:48 -0600 (MDT), Warren Block wrote: > I think the Crucial M550 SSDs have additional backup capacitors also. > However, I'm still skeptical about the value of a small SSD power backup > versus a true UPS for the entire system. I have read an interesting article on this topic: http://www.anandtech.com/show/8528 Micron M600 (128GB, 256GB & 1TB) SSD Review (The Truth About Micron's Power-Loss Protection) The latter part of this article reports Micron's position of this specific function. In my understanding, Micron's consumer-class SSDs such as M550 have very small backup capacitors which would not be worth flushing dirty DRAM cache, but completing ongoing NAND programming. This means while programming at power loss would not corrupt NAND, "successfully written" host write would be lost due to cache loss. It does not provide enough peace of mind required for logging device. It looks like metadata journaling or softupdates for filesystem, not a full journaling implementation. -- kuro
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?864mvigtxd.wl%poyopoyo>