Re: time limited error recovery and md raid

[Redeeman <redeeman@metanurb.dk>]

On Fri, 2008-12-05 at 16:12 -0500, Justin Piszcz wrote:
> 
> On Fri, 5 Dec 2008, Redeeman wrote:
> 
> > On Fri, 2008-12-05 at 16:01 -0500, Justin Piszcz wrote:
> >>
> >> On Fri, 5 Dec 2008, Redeeman wrote:
> >>
> >>> Hello..
> >>>
> >>> Im going to be building a software raid6 setup with probably 8 disks,
> >>> and i've been looking at the wd gp disks, which comes in both standard
> >>> and raid edition, with the raid edition being much more expensive.
> >>>
> >>> I have searched around, and found that it is indeed possible to activate
> >>> tler on the "normal" disks, however, the setting has a parameter, more
> >>> specifically, how many seconds it should be limited to. Default is 7.
> >>>
> >>> So i was wondering, what should that be set to, to be optimal for linux
> >>> md raid? i havent been able to find any information about this.
> >>>
> >>>
> >>> Thanks.
> >>>
> >>>
> >>> mvh.
> >>> Kasper Sandberg
> >>>
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> >>>
> >>
> >> The exact time is a good question.
> >>
> >> Something I have noticed is when TLER is off, the drives hang up when they
> >> hit a bad sector and when TLER is on, the drives is kicked out of the
> >> array immediately when it reports a bad sector.
> >
> > First.. Does this happen with a degree of frequency on these disks? you
> > recommend other disks?
> The disks I have are velociraptors, I will be reverting back to my old 
> raptor150s shortly to ensure everything is fine with them before I go 
> buying new hard drives, etc.  It happened every week or two with 
> velociraptors, bad drives or drives getting kicked out of the array over 
> and over again.
> 
> > second, when tler is off, it hangs FOREVER? or just until it gives up?
> When TLER is off it hangs for 1-2 minutes and then you will see a timeout 
> in the dmesg/kernel log and it (sometimes) kicks the drive out of the 
> array, othertimes it 'hard' resets the drive the array is able to continue 
> operating normally.
> 
> > when tler is on, why does linux not attempt to remap the sector?
> See my earlier posts on this question from last week.  It would need a 
> metadata section on each HDD to keep track of the bad sectors before it 
> writes to the drives, a 3ware card will do this for you-- however, 
I thought disks had this internally, and could be prompted to do it by
writing to the sector?
> typically, (having run md/linux) for a number of years is not 
> super-necessary if you run checks on your disks once a week *AND* you have 
> good drives that don't have problems.
Obviously i intent to replace broken disks as i detect them, but as i
understand it, its fairly common case that disks will get bad sectors
over time, and remap them internally?
> 
> Justin.
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