Date: Thu, 24 Jan 2013 09:32:58 +0100 From: Borja Marcos <borjam@sarenet.es> To: Jean-Yves Moulin <jym@baaz.fr> Cc: FreeBSD Filesystems <freebsd-fs@freebsd.org>, Scott Long <scottl@samsco.org> Subject: Re: RFC: Suggesting ZFS "best practices" in FreeBSD Message-ID: <8BA7B786-3B4B-473B-B4F0-798C9B5AEF00@sarenet.es> In-Reply-To: <81460DE8-89B4-41E8-9D93-81B8CC27AA87@baaz.fr> References: <314B600D-E8E6-4300-B60F-33D5FA5A39CF@sarenet.es> <565CB55B-9A75-47F4-A88B-18FA8556E6A2@samsco.org> <81460DE8-89B4-41E8-9D93-81B8CC27AA87@baaz.fr>
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On Jan 23, 2013, at 4:16 PM, Jean-Yves Moulin wrote: > But what about battery-backed cache RAID card ? They offer a non-volatile cache that improves writes. And this cache is safe because of the battery. These feature doesn't exist on bare disks. They can be "fine" for certain applications, especially with limited ability filesystems. But we are speaking about using maybe the latest and greatest in filesystem technology, with a superior mechanism to manage redundancy and I/O bandwidth. Using another redundancy mechanism underneath can make matters worse, with one system working against the other. ZFS manages it better. ZFS allows you to decide if you need to cache metadata and/or data or none of them. RAID cards can show stupid caching behaviors depending on your workload. So, RAID card with ZFS, definitely a no-no. As Scott said, more failure modes. And some of them, complex. Many trivial operations may require a reboot. The card hides important disk diagnostics from ZFS. Borja.help
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