Re: [Xen-users] how to start VMs in a particular order

[lee <lee@xxxxxxxxxxxxxxx>]

"J. Roeleveld" <joost@xxxxxxxxxxxx> writes:

> On Thursday, July 03, 2014 04:03:26 AM lee wrote:
>> Joost Roeleveld <joost@xxxxxxxxxxxx> writes:
>> > On Tuesday 01 July 2014 23:48:51 lee wrote:
>> >> Joost Roeleveld <joost@xxxxxxxxxxxx> writes:
>> >> > Check the howtos for smartctl, they explain how to interpret the data.
>> >> > I'd recommend:
>> >> > http://www.smartmontools.org/
>> >> 
>> >> Ok, if I get to see the numbers, I can look there.  I never believed in
>> >> this smart thing ...
>> > 
>> > You just wait for disks to die suddenly?
>> 
>> yes
>> 
>> You stock up on new disks just because smart might tell you that your
>> disks will die eventually?
>
> No, when SMART shows errors that indicate a dying disk, I order a 
> replacement. 
> When it arrives, I swap the disk. The dying disk then either gets send back 
> for warranty, or used for testing.

You must have some really good warranties to get them exchanged because
of what smart values they show.  It's a moot point, though; I can't give
a disk out of hand once my data was on it without physically destroying
it first, and when you do that, they won't replace it :(

And you must have a lot of money to waste disks like that.  How many of
these disks were actually bad or would have gone bad within a week or
two if you hadn't replaced them?  How many within a year?

>> >> You have seen three (or more) disks going bad all at the same time just
>> >> because they were connected to a different controller?
>> > 
>> > Yes,
>> 
>> And smart didn't tell you they would go bad? ;)
>
> SMART didn't exist back then.

It wouldn't have shown you if it had existed.

>> I'll keep this in mind ... and in the future, I might as well connect
>> defective disks to unknown controllers before good ones to see if the
>> controller kills them.
>
> This was around 1998, I wouldn't expect dodgy hardware like that anymore. 
> Especially not from products used by bigger companies.

Why not?  I wouldn't have expected it in 1998, and I don't expect it
today.

>> > For twice that, I got 3TB WD Red drives a few years ago, after the
>> > factories came back online.
>> 
>> Are they twice as good?  I know they're quite a bit faster.  However,
>> when I bought the WD20EARS, there weren't any red ones, only RE ones,
>> which, IIRC, cost about 4 times as much as the WD20EARS.  That was just
>> too much.
>
> I agree, the RE ones are too expensive.
> They are a lot faster, instead of taking a week(!) to build the Raid-6 array 
> with 6 disks, it now takes 20 hours.
> Both figures with the 3TB versions.

That's quite a difference!  Are you comparing the red ones with the RE
ones?

>> >> without a backplane in the way.  It is probably true that IBM --- and/or
>> >> Adaptec
>> > 
>> > I believe you are using an IBM raid controller. Not an Adaptec part. At
>> > least, I can't see Adaptect in any of the documentation I saw online.
>> 
>> It's an IBM when you go by the labels and documentation.  Apparently
>> Adaptec made it (for IBM).
>
> But who wrote the firmware?

You'd have to ask IBM or Adaptec ... I'd guess they might have worked
together on it.

>> It's rather weird because it's a card that plugs into a special slot,
>> with apparently some/most of the controller integrated into the board.
>> Without the board, that card is useless.
>
> If you remove the card, can you still see the drives from an OS?

Hm, I wouldn't think of trying that.  I'd have to try and see what
happens.

>> Hm, did you find any documentation about it?  It would appear to be an
>> IBM-ESXS VSC7160 enclosure, and I haven't found any documentation for
>> it.  Apparently there are various drivers for it --- why would those be
>> needed?
>
> My info was based on that page and from what I can see on pictures.
> I see a single SAS-port on the mainboard. If that is all that is connected to 
> the backplane (enclosure), then either a PMP is used. Or only 4 disks can be 
> used.

There's a port at the back of the case to connect external drives.  From
pictures, I thought there's one or two ports on the RAID card.  Two
ports would make sense because it would probably allow 8 disks, and
there have been different versions of the same model with slots for more
disks.

I might give it a close look next time it's shut down.  It doesn't
really matter since I don't have any (reasonable) way of installing
disks other than sliding them into the enclosure the way it's supposed
to be.

> The drivers might be needed for:
> 1) The PMP
> 2) Reading some environmental values
> 3) Some other function

Fortunately, it works without.  There's an independent controller for
the environmental functions and whatever else it may control, and I can
see and do some things with a web browser because there's an independent
management card.

>> > SAS and SATA controllers often talk about sata channels. My raid
>> > controller
>> > even still calls them IDE-channels. It's just a name.
>> 
>> It's obfuscating --- a better explanation would be much more helpful.
>
> It's sticking to old names. As long as I can identify the drives using the 
> name (IDE1, IDE2,...), I don't care much about the name given.

In this case, it's not sufficient.  When you look at the documentation,
you don't see any point to have "different SATA channels" visible, let
alone adjustable, by the user.  There's no mention of what you should
set other than that 0 is the default and supposed to work best.
Instead, you're being referred to some mysterious thing they call AMSU
which you should not update unless you can't avoid it, and you can't
even figure out how to update it.

It is a feature that does need clear explanation, and they're not giving
any.  The documentation should also say what the difference between
these PHY settings is.

>> >> So for what's it worth:  For WD20EARS on a ServeRaid 8k, try different
>> >> PHY settings.  PHY 2 seems to work much better than 0, 1 and 5.
>> > 
>> > That is usefull news, especially if that keeps the system running. Maybe
>> > post that online somewhere, including on that page?
>> 
>> That was my intention :)  There are archives of this mailing list,
>> aren't there?
>
> Yes, including on my mail server. But not everyone might find this mailing 
> list at some point.

No matter where I put this information, not everyone might find it.  So
where should it be?

>> How would the RAID controller know which disk is in which slot when they
>> are all behind a PMP?  It does know that.
>
> It will need to, how else can it tell you which disk to replace?
> If it only gives you the port on the raid card, you need to test all disks 
> behind the PMP to find out which one died...

Yes, and how does it know?

>> 3 Gbit/sec divided by 8 gives you Gbytes/sec, i. e. 0.375.  That's 375
>> MB/sec.  There's some protocol overhead, so you can keep up with three,
>> perhaps four disks, and you can't with six.
>
> Not if you have a lot of constant I/O. I only know of a few types of usage 
> where that happens. Storing data from sensor equipment is one of them, but 
> for 
> those situations, you wouldn't use PMPs.
>
> I don't see an issue with most usage, provided you use components 
> (controller, 
> PMP, disks) that support all the nice features that help performance.

You think a single port would keep up with up to 6 (or 8 in different
models, if not more) SAS disks?

>> > I hope setting 2, as you mentioned above, keeps it stable.
>> 
>> It still hasn't crashed yet :)  I wonder if 3 or 4 might be better ...
>
> It's your hardware and data. But if it were me, I would keep it on 2 :)

I wouldn't test it without a backup :)


-- 
Knowledge is volatile and fluid.  Software is power.

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