From e20bc696cb45f0f84e5cc8e5c8cd3b2ca1b63685 Mon Sep 17 00:00:00 2001 From: uqs Date: Thu, 5 Jan 2012 21:36:20 +0000 Subject: Document the detrimental effect of kern.cam.XX.retry_count for recoverdisk(1) recoverdisk(1) wants to know about read errors when doing the 1MB/64k reads as fast as possible so it can continue and retry them later with smaller reads (down to sector size). Any retries by lower layers will only slow it down. Prodded by: arundel --- sbin/recoverdisk/recoverdisk.1 | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) (limited to 'sbin/recoverdisk') diff --git a/sbin/recoverdisk/recoverdisk.1 b/sbin/recoverdisk/recoverdisk.1 index 9eff8f7..044b801 100644 --- a/sbin/recoverdisk/recoverdisk.1 +++ b/sbin/recoverdisk/recoverdisk.1 @@ -24,7 +24,7 @@ .\" .\" $FreeBSD$ .\" -.Dd May 1, 2011 +.Dd Jan 5, 2012 .Dt RECOVERDISK 1 .Os .Sh NAME @@ -124,7 +124,11 @@ recoverdisk -b 0 /dev/ad3 /somewhere .Ed .Sh SEE ALSO -.Xr dd 1 +.Xr dd 1 , +.Xr ada 4, +.Xr cam 4, +.Xr cd 4, +.Xr da 4 .Sh HISTORY The .Nm @@ -149,6 +153,18 @@ flying by. This is harmless and can be avoided by setting .Fl b to no more than 128kB. +.Pp +.Nm +needs to know about read errors as fast as possible, i.e. retries by lower +layers will usually slow down the operation. +When using +.Xr cam 4 +attached drives, you may want to set kern.cam.XX.retry_count to zero, e.g.: +.Bd -literal +# sysctl kern.cam.ada.retry_count=0 +# sysctl kern.cam.cd.retry_count=0 +# sysctl kern.cam.da.retry_count=0 +.Ed .\".Pp .\"When reading from optical media, a bug in the GEOM framework will .\"prevent it from seeing that the media has been removed. -- cgit v1.1