Date: Sat, 10 Jan 2009 13:38:30 +1100 From: Andrew Snow <andrew@modulus.org> To: fbsd@dannysplace.net, freebsd-fs@freebsd.org Subject: Re: Areca vs. ZFS performance testing. Message-ID: <49680A26.1020502@modulus.org> In-Reply-To: <496712A2.4020800@dannysplace.net> References: <20081031033208.GA21220@icarus.home.lan> <491C5AA7.1030004@samsco.org> <491C9535.3030504@dannysplace.net> <CEDCDD3E-B908-44BF-9D00-7B73B3C15878@anduin.net> <4920E1DD.7000101@dannysplace.net> <F55CD13C-8117-4D34-9C35-618D28F9F2DE@spry.com> <20081117070818.GA22231@icarus.home.lan> <496549D9.7010003@dannysplace.net> <b072dc420901072348n7d094937u89b6d24959f8ae3d@mail.gmail.com> <4966B6B1.8020502@dannysplace.net> <b072dc420901090046v77bc5407xacda5e65fc6ad7bf@mail.gmail.com> <496712A2.4020800@dannysplace.net>
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ZFS does not require battery-backed disk cache, as long as disks and controller flush their cache when they are told to by the OS. Then ZFS only issues sync/flush commands for the ZIL (transaction log), but majority of I/Os are free to sit in cache to complete when they are ready. Data that is not fsync()'d by the application may be lost on power outage, but stuff like databases do fsync() so they are protected. - Andrew
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