Date: Tue, 21 Sep 2010 15:38:22 -0700 From: David Brodbeck <gull@gull.us> To: freebsd-fs@freebsd.org Subject: Re: what happens to pool if ZIL dies on ZFS v14 Message-ID: <AANLkTikEgrFGGUVUW8dQWGH44K41jPG=PwXXzsT5fYdV@mail.gmail.com> In-Reply-To: <20100917161847.GA58503@icarus.home.lan> References: <AANLkTi=vYVG300nhMjkcLju=kQhBdPJDqyaXR0mG84%2Bp@mail.gmail.com> <4C9385B0.2080909@shatow.net> <AANLkTin0LwQz%2BWi5cBOcHuVqyOz3%2BfFR7YC_=f2L5CyX@mail.gmail.com> <AANLkTinbPK1rNK5hg=t7N=sqFLuh8sNrZT9DFC_ppXWF@mail.gmail.com> <20100917161847.GA58503@icarus.home.lan>
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On Fri, Sep 17, 2010 at 9:18 AM, Jeremy Chadwick <freebsd@jdc.parodius.com> wrote: > Given the severity of this predicament, then why is it people are > disabling the ZIL (via vfs.zfs.zil_disable=1) ? If you don't have a separate log device, synchronous writes are very slow with the ZIL enabled. This isn't such a big deal unless you're using NFS, where essentially every write is synchronous. Then many common operations become conspicuously slow, especially compared to Linux, which isn't as fastidious about requiring data to be flushed all the way to the platters before signaling to NFS clients that the operation is complete. The danger in this case isn't that the pool could be damaged, but that a server crash could result in data not being written to disk even though the client believes the operation completed successfully; essentially, this would be silent data loss, since NFS server reboots are supposed to be invisible to client applications.
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