unable to boot now that one drive went bad in dual boot config

In message , Paul
writes:
[]
You can tell I'm conservative on these things, because
*none* of my retired drives is dead. None have
a CRC error yet (i.e. a sector that could not be
reallocated because no nearby spares are left).
I try my best to extrapolate "where a drive is going",
but they continue to surprise me, every time I
run scans.

Paul

(Me too.) I'm intrigued by your use of the word "nearby" above: do you
mean that drives only reallocate to _nearby_ sectors? I'd understand if
they choose those _first_. (It hadn't occurred to me to wonder about the
distribution of the spares: I suppose spread out _would_ be best. If
anything, I'd thought they were all at the end.)

Do reallocated sectors themselves get reallocated if they go bad, or is
it only a one-level thing? Or does it vary between makes/models?

(Do you have those figures (TBW and hours-per-year-powered) for my HGST
HTS541010B7E610 drive [now 345 hours]?)
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

"There are a great many people in the country today who, through no fault of
their own, are sane." - Monty Python's Flying Circus

J. P. Gilliver (John) wrote:
In message , Paul
writes:
[]
You can tell I'm conservative on these things, because
*none* of my retired drives is dead. None have
a CRC error yet (i.e. a sector that could not be
reallocated because no nearby spares are left).
I try my best to extrapolate "where a drive is going",
but they continue to surprise me, every time I
run scans.

Paul

(Me too.) I'm intrigued by your use of the word "nearby" above: do you
mean that drives only reallocate to _nearby_ sectors? I'd understand if
they choose those _first_. (It hadn't occurred to me to wonder about the
distribution of the spares: I suppose spread out _would_ be best. If
anything, I'd thought they were all at the end.)

Do reallocated sectors themselves get reallocated if they go bad, or is
it only a one-level thing? Or does it vary between makes/models?

(Do you have those figures (TBW and hours-per-year-powered) for my HGST
HTS541010B7E610 drive [now 345 hours]?)

If a reallocated sector is on the same track, it can be sitting in
the track buffer on a read. That means there will be minimal
interference with performance, if the sector that happens to be
spared out, is "nearby".

IBM at least, used to keep the sector mapping in the cache RAM,
to translate "from-to" and figure out which LBA is the one
they need to use as the space.

To have to head switch to get a sector, costs 1 millisecond
for the head switch, plus the rotation time to get to the sector.
So you really don't want to switch platters to get your spare.

And to the best of my knowledge, they don't leave all the heads
running in parallel on a read. Like if you had four platters and
eight heads, if there was enough bandwidth at the controller,
you could put all eight tracks in the track buffer. But I don't
think the RAM is currently fast enough. The RAM usually isn't
the most modern version, merely the cheapest version they can
get in bulk.

I've not seen any info on the "locality" of spares, but if you
move them too far away from the trouble area, it's going to make
the drive really slow.

And if a drive has sectors sitting in "Current Pending" status,
they stay there until the sector is written. Then the drive can
decide whether to spare them out or not. If a sector like that
sits in Current Pending, it can take *fifteen seconds* worst
case to read it. It takes less time on RE drives with TLER
enabled, which reduces the retries below the RAID timeout
constant. The RAID timeout constant is a lot less than 15 seconds.

So if you have a drive that's looking bad in any case, it probably
wouldn't hurt to back it up, "Clean All" from end to end,
do the restore, just to get all the trouble maker sectors spared
out. Then see if the drive has any "health" left in SMART.

I don't really retire drives when they're broken, I
retire them when they annoy me :-)

Paul