Date: Tue, 16 Sep 2014 22:09:08 +0800 From: Xin Li <delphij@delphij.net> To: Xu Zhe <xzpeter@gmail.com>, freebsd-scsi@freebsd.org Subject: Re: How to disable hard disk write cache? Message-ID: <54184484.1070304@delphij.net> In-Reply-To: <541804B0.7070407@gmail.com> References: <541804B0.7070407@gmail.com>
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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 On 9/16/14 5:36 PM, Xu Zhe wrote: > Hi, all, > > Does anyone knows how to disable write cache of hard disk? > > I have found some hints here at Freebsd website: > > https://www.freebsd.org/doc/handbook/configtuning-disk.html > > However, this seems only work for ATA devices, what about SAS/NLSAS > devices (Meanwhile, it seems that there is no such sysctl in latest > Freebsd release, which is 10.0)? > > Any hints are welcomed! Why do you want to disable write cache in the first place? It's not needed for most configurations nowadays. Modern SATA/SAS/SCSI devices usually comes with the capability of tagged commands, allowing the OS to know when a write buffer is on stable storage. With this, file systems can easily implement the right semantics and recover from e.g. a power outage, etc. Cheers, -----BEGIN PGP SIGNATURE----- iQIcBAEBCgAGBQJUGESDAAoJEJW2GBstM+ns2R4QAKKL2+TKfTaFQOWk4/jOKzdD 6yANm2ZYI3reChuUmbYjjchfce6nGcxz7EPjTOfBLj37p8bZFaW91e/ayviY9pNL QktP0hgTZp4EFLJSlPfqjx6f8aU2gJ640b/cKbIQkaxHWRLoHea8GJ2XhyVS9JfK o8aM+VPyxRrTRH0e2BQ8t0DMJohCrVNZ0fYSAKToDqI2RpcmOumYA4yChXb0hgvc Rz3PGZth19E4rxdNtOM0Ap/l4PL3+lInIlU8kPdwUaqvT11mxjUM+6zkF904VtqL 5xoURW/j9MAbFl6ozJJKnkfd20lCT3TfyQUC7weDOT8Jz78/8Sx2qy6ilkQCe0ZI AWV0hpoQPk2bzFxwB7wr9MiVbXJcpAHfHFcKTbLWY4NzY/8RknDt5dNsqsntlDww dSb1xRLdPQFBh7NrZA1GAfxXdfK8GNBONF+cRKutvFAlIzq0kywaa5baN1ZwLdU2 Kz3LJ0SLQMNEFioES+9j94fSeiW9LY9OJlI9EAjf2gys4WFeLkTgOgdBhvY935Mi j6FHk4xZmgKOS2s0c7UOYMjj6OgU1or4t2awMF/ObQwd8cmCT5abeGUdtrDGdCZu am/9nbCfR6FHhm5k90t+yCzl/hPf7dqVoz41bnP6+dD5q5zwxOhOc/SEiCJKCH3L iQoPiJfxH7JGZdCw/Vz+ =QSHo -----END PGP SIGNATURE-----
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