>>> The big advantage to adding disks virtually instead of physically is
>>> that you are not limited by the form factor of the server, the power
>>> output of the PSUs and most importantly, they can be done on the fly,
>>> without having to take an outage.
>>
>> But you still need to (at a minimum) reboot the server after you change
>> the SAN mapping anyway.
>
> Obviously, Windows may complain if you try to pull the C: drive from
> under its feet, but you shouldn't actually boot from a SAN drive under
> normal circumstances anyway.

Oh, I see. Well, if you're not changing the OS partition, then yes, that 
should work.

>>> In your environment, it may not be that big of an issue, but when you
>>> have contracted service level agreements that you will have 99.99%
>>> uptime, you have no other choice. Do the math, that means 1m42s of
>>> downtime per month... try powering off a server, taking it out of the
>>> rack, adding a disk and powering it back on in less than 10 times that!
>>
>> Uhuh. And when one server physically dies, it's going to be down a tad
>> longer than 1m42s. So if you don't have the spare capacity to handle
>> that, a SAN still hasn't solved your problem.
>
> Need help moving those goalposts? They look heavy! We weren't talking
> about a server dying. We were talking about needing more disk space.

That was not clear to me. You made it sound like "hey, if you have a 
SAN, then when one data centre dies, you can just use the other one!" 
You're going to need more than just a SAN to do that.

I would have thought that needing more disk space is such a crushingly 
rare event that it makes almost no sense to optimise for it. If you have 
to take a server offline once every 5 years to add another disk, that's 
still 99.99% uptime.

>> This makes no sense at all. How the hell can a 6 Gbit/s SATA link
>> perform the same as a 100 Mbit/sec Ethernet link? Never mind a 10
>> Mbit/sec Internet link. That makes no sense at all. (Unless your actual
>> disks are so feeble that all of them combined deliver less than 10
>> Mbit/sec of data transfer speed...)
>
> You're making a strawman argument. No one ever said that SANs run over
> 10Mbit ethernet.

Neither did I. I said 100 Mbit Etherhet. (It's quoted right there.)

You claimed that it's not insane to run a SAN over the Internet, despite 
the fact that typical Internet speeds are roughly 10 Mbit/sec or slower.

> most SAN implementations run dedicated protocols over
> fibre at Gbps speeds.

It's news to me that such things even exist yet - but perhaps that was 
your point?

Still, it looks like the UK site will soon be in possession of their 
very own SAN, so I guess I'll be able to watch it fail up close and 
personal. o_O

> Four 9s and Five 9s uptime is expensive.

Hell yes.

Actually, I think we can simplify this to "uptime is expensive". I've 
yet to see a method of improving uptime that's cheap.

>> For that, you would need [at least] two geographically remote sites
>> which duplicate everything - disk and other hardware as well. I'm
>> struggling to think of a situation where the volume of data produced per
>> hour is so low that you can actually keep it synchronised over the
>> Internet. And if it isn't in sync, then a failover to from primary to
>> secondary system entails data loss.
>
> Not the Internet, multiple dedicated 10Gbps DWDM links. You'd be
> surprised to know that most Fortune 1000 entreprises actually do this
> already.

So what you're saying is that a handful of the richest companies on 
Earth can afford to do this? Yeah, I guess that'll be why I haven't seen 
it before. :-P

>>> That's because you keep forgetting that other people may have other
>>> needs than yours.
>>
>> Perhaps. But saying "we work in the financial industry" doesn't tell me
>> how your needs are different than mine. Really, the only way you'd truly
>> come to understand this is by actually /working/ in that industry. And
>> that's just not possible.
>
> Are you saying it's impossible to work in the banking industry? Or are
> you saying that the banking industry is so secretive about their work
> that you can't even find out how they operate without working there?

I'm saying it's not possible to go work in every random industry just to 
find out what makes it tick.

> Of course, you can also decide that it's not worth it to learn about
> these things and simply shrug it off, but don't complain that you can't
> get jobs outside of the little hole you dug yourself into.

I didn't say it's not possible to get a job, I said it's not possible to 
get insight without getting a job.

Post a reply to this message

Le 2012-02-01 11:45, Invisible a écrit :
>>>> The big advantage to adding disks virtually instead of physically is
>>>> that you are not limited by the form factor of the server, the power
>>>> output of the PSUs and most importantly, they can be done on the fly,
>>>> without having to take an outage.
>>>
>>> But you still need to (at a minimum) reboot the server after you change
>>> the SAN mapping anyway.
>>
>> Obviously, Windows may complain if you try to pull the C: drive from
>> under its feet, but you shouldn't actually boot from a SAN drive under
>> normal circumstances anyway.
>
> Oh, I see. Well, if you're not changing the OS partition, then yes, that
> should work.
>
>>>> In your environment, it may not be that big of an issue, but when you
>>>> have contracted service level agreements that you will have 99.99%
>>>> uptime, you have no other choice. Do the math, that means 1m42s of
>>>> downtime per month... try powering off a server, taking it out of the
>>>> rack, adding a disk and powering it back on in less than 10 times that!
>>>
>>> Uhuh. And when one server physically dies, it's going to be down a tad
>>> longer than 1m42s. So if you don't have the spare capacity to handle
>>> that, a SAN still hasn't solved your problem.
>>
>> Need help moving those goalposts? They look heavy! We weren't talking
>> about a server dying. We were talking about needing more disk space.
>
> That was not clear to me. You made it sound like "hey, if you have a
> SAN, then when one data centre dies, you can just use the other one!"
> You're going to need more than just a SAN to do that.
>

No. I said that if you have two SANs in separate data centres, with data 
replicated on both data centres, then it greatly reduces your down time 
in case of a disaster.  I never claimed that all SANs were designed that 
way, nor that it was the only requirement for instant recovery.

> I would have thought that needing more disk space is such a crushingly
> rare event that it makes almost no sense to optimise for it.

No it's not.  You may need to run an app in debug mode for a while and 
need extra space to store the dumps.  You may run into seasonal peeks 
and need extra storage just for that period. Etc...  Sizing hundreds of 
servers for a worst case scenario is not efficient use of the company's 
money.  You are much better off having some amount of slack space that 
you can swing around when needed.

> If you have
> to take a server offline once every 5 years to add another disk, that's
> still 99.99% uptime.
>

Not if your contract says "monthly uptime of 99.99%". ;-)

>>> This makes no sense at all. How the hell can a 6 Gbit/s SATA link
>>> perform the same as a 100 Mbit/sec Ethernet link? Never mind a 10
>>> Mbit/sec Internet link. That makes no sense at all. (Unless your actual
>>> disks are so feeble that all of them combined deliver less than 10
>>> Mbit/sec of data transfer speed...)
>>
>> You're making a strawman argument. No one ever said that SANs run over
>> 10Mbit ethernet.
>
> Neither did I. I said 100 Mbit Etherhet. (It's quoted right there.)
>
> You claimed that it's not insane to run a SAN over the Internet,

When did I say that?

> despite
> the fact that typical Internet speeds are roughly 10 Mbit/sec or slower.
>
>> most SAN implementations run dedicated protocols over
>> fibre at Gbps speeds.
>
> It's news to me that such things even exist yet - but perhaps that was
> your point?
>

Actually, it shouldn't be news to you.  We went over this in great 
details a few months ago.  Remember my nice ascii-graphics chart with 
the servers, SAN switches, drive enclosures and tape units?

> Still, it looks like the UK site will soon be in possession of their
> very own SAN, so I guess I'll be able to watch it fail up close and
> personal. o_O
>

Not that SANs are infaillible, but why do you assume that it will fail?

>> Four 9s and Five 9s uptime is expensive.
>
> Hell yes.
>
> Actually, I think we can simplify this to "uptime is expensive". I've
> yet to see a method of improving uptime that's cheap.
>
>>> For that, you would need [at least] two geographically remote sites
>>> which duplicate everything - disk and other hardware as well. I'm
>>> struggling to think of a situation where the volume of data produced per
>>> hour is so low that you can actually keep it synchronised over the
>>> Internet. And if it isn't in sync, then a failover to from primary to
>>> secondary system entails data loss.
>>
>> Not the Internet, multiple dedicated 10Gbps DWDM links. You'd be
>> surprised to know that most Fortune 1000 entreprises actually do this
>> already.
>
> So what you're saying is that a handful of the richest companies on
> Earth can afford to do this?

There's more than a handful of companies who can afford it.  A few £M in 
extra telco costs per year is nothing compared to the prospect of going 
out of business because your data centre had a 110-story building crash 
on top of it.

 > Yeah, I guess that'll be why I haven't seen it before. :-P

I have never seen the Merryll-Lynch data centre first hand, either, but 
that isn't necessary to know that they were back up and running hours 
after the WTC towers fell... Reading the story of how they restarted 
their operations from their disaster recovery location was enough.  Then 
the "Interesting...how'd they manage that?" questions popped up in my 
head, and I started digging...

Which is the main point of this whole discussion: reading the newspaper 
and other news-related web sites, once in a while, is not a bad thing, 
even if the event in question doesn't affect you directly, there may be 
bits of insight to be gathered.

-- 
/*Francois Labreque*/#local a=x+y;#local b=x+a;#local c=a+b;#macro P(F//
/*    flabreque    */L)polygon{5,F,F+z,L+z,L,F pigment{rgb 9}}#end union
/*        @        */{P(0,a)P(a,b)P(b,c)P(2*a,2*b)P(2*b,b+c)P(b+c,<2,3>)
/*   gmail.com     */}camera{orthographic location<6,1.25,-6>look_at a }

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On 1-2-2012 17:45, Invisible wrote:

>> Of course, you can also decide that it's not worth it to learn about
>> these things and simply shrug it off, but don't complain that you can't
>> get jobs outside of the little hole you dug yourself into.
>
> I didn't say it's not possible to get a job, I said it's not possible to
> get insight without getting a job.

This was a more general remark. We know that you are in a job where you 
are not happy and that is probably below your capacities. At the same 
time you repeatedly show that you are not interested in a wider view on 
the field you work in. In this field you have to read a number of 
different sources to get a feeling for what direction the industry is 
taking (or if you are realy good: what direction it will be taking in a 
couple of years). If you don't develop yourself there is no way you will 
ever get a job elsewhere and it is quite likely that you loose the one 
you have as soon as a competent manager enters. I know it is unlikely, 
but such persons do exist, although few and far between, so you still 
have a chance.

In short you have to choose: complain about your job or complain about 
all sorts of technologies that you were not aware of, but you can not do 
both.


-- 
tip: do not run in an unknown place when it is too dark to see the 
floor, unless you prefer to not use uppercase.

Post a reply to this message

On Tue, 31 Jan 2012 09:12:09 +0000, Invisible wrote:

>>>> It's easier to find jobs to apply to when you have a broader
>>>> awareness of the world than just what's relevant to you right now.
>>>
>>> I doubt you're going to get that by reading some text on a screen. To
>>> understand what a new capability means, you often need to experience
>>> it for yourself.
>>
>> Hmmm, so let me see if I understand this correctly....You're asserting
>> that one of the methods that I actually use to keep up on technology
>> doesn't work?  Interesting that you'd have insight into what works for
>> me on such a deep level.
> 
> I'm saying that if (for example) I read somewhere that a lot of
> companies use Citrix to host their applications, that doesn't really
> qualify me for a job managing Citrix. If I had actually /used/ Citrix,
> or something vaguely like it, then yes. But having read about how it
> exists and people use it? Not so much, no.

Knowing about the trend, though, in the use of Citrix for telecommuting 
(for example) is something that's actually useful.  No, it doesn't 
qualify you to manage a Citrix system - but that's not the point.  The 
point is not looking like you're not aware of the trend when asked about 
it in an interview.

Combine a demonstrated ability to quickly assimilate technologies with an 
awareness of what's going on with the industry, and that is something 
that looks good.

But if you're unaware of what Citrix even *does*, then that calls into 
question (in an interview) whether you even know what's going on in IT.

>>> OK, I have to ask: What the hell is this "RSS" everybody keeps
>>> mentioning?
>>
>> Google it.  If that doesn't work, try "Really Simple Syndication". 
>> It's only all over the web.
> 
> Ooo, because I haven't tried *that* before. :-P
> 
> OK, so let's see... First hit from Google is
> 
> http://en.wikipedia.org/wiki/RSS
> 
> (Unless you meant Royal Statistical Society, which I'm pretty sure you
> didn't.)
> 
> As usual with Wikipedia, the page babbles about updates and feeds and
> XML and "syndication" and something about RDF, but utterly fails to
> explain WHAT IT IS.


<sigh>

From wikipedia:

--- snip ---

RSS feeds benefit publishers by letting them syndicate content 
automatically. A standardized XML file format allows the information to 
be published once and viewed by many different programs. They benefit 
readers who want to subscribe to timely updates from favorite websites or 
to aggregate feeds from many sites into one place.

RSS feeds can be read using software called an "RSS reader", "feed 
reader", or "aggregator", which can be web-based, desktop-based, or 
mobile-device-based. The user subscribes to a feed by entering into the 
reader the feed's URI or by clicking a feed icon in a web browser that 
initiates the subscription process. The RSS reader checks the user's 
subscribed feeds regularly for new work, downloads any updates that it 
finds, and provides a user interface to monitor and read the feeds. RSS 
allows users to avoid manually inspecting all of the websites they are 
interested in, and instead subscribe to websites such that all new 
content is pushed onto their browsers when it becomes available.

--- snip ---

Now, I read your blog and keep up on it by using - that's right - an RSS 
feed.  I have the feed set up in Google Reader so that when you post 
something new on your blog, I see it as part of the Reader page.

That way I don't have to visit your blog to see what's going on in your 
blog.  I see an item show up in my reading list so, as wikipedia says, I 
"avoid manually inspecting all of the websites [I] am interested in" and 
can see what's new.

>>> I usually visit Tom's Hardware when I want to see what's happening in
>>> the hardware world.
>>
>> I doubt you're going to get that by reading some text on a screen.
> 
> That's why I just built a new PC - to experience the Core i7 first-hand.
> :-P

So then why bother going to Tom's Hardware again?

> The BBC's iPlayer system "works". I mean, it's so horrifyingly blurry
> that you sometimes can't see people's faces clearly enough to recognise
> who's who, and often the end credits are unreadable. But technically
> that still counts as "works", right?

I don't know what kind of connection you use, but I stream on iPlayer 
occasionally from halfway around the world (did that with last night of 
the proms IIRC) and projected it onto a 10' screen.  Didn't look 
particularly blurry to me.

> 
> I just looked it up. The transfer rate of a DVD is 10.5 mbit/sec. The
> maximum broadband speed you can get is 8 mbit/sec. So... does that mean
> that people in America have something faster than ADSL or something?

I don't - I have 3 Mbps down ADSL.  I have to not be doing other things 
with the network connection when I'm streaming Netflix, but I do get a 
high quality HD image with 5.1 sound with programmes that include it.

But more to the point, do you now understand what streaming is?

Jim

Post a reply to this message

On Wed, 01 Feb 2012 16:45:18 +0000, Invisible wrote:

>> Of course, you can also decide that it's not worth it to learn about
>> these things and simply shrug it off, but don't complain that you can't
>> get jobs outside of the little hole you dug yourself into.
> 
> I didn't say it's not possible to get a job, I said it's not possible to
> get insight without getting a job.

That's simply not true.

Case in point:  I worked as a system administrator and systems engineer 
for years.  Then I moved into technical training and education.  I had no 
formal background in technical training, course development, etc.  So I 
talked to people in that line of work before moving into it to see if it 
was something I might be good at.

I got insight without getting the job.

Similarly, I've never been a software engineer before, but I've gotten 
insight into how things like SCRUM and Agile work by talking to people 
who use them on a daily basis.  Again, no job, but insight.

Jim

Post a reply to this message

On 1/31/2012 1:12, Invisible wrote:
> As usual with Wikipedia, the page babbles about updates and feeds and XML
> and "syndication" and something about RDF, but utterly fails to explain WHAT
> IT IS.

I have to ask... Do you start reading at the beginning of the article, or do 
you skip over the part that comes before the table of contents or something?

First sentence in the article:

"RSS ...  is a family of ... formats used to publish frequently updated 
works ... in a standardized format."

How is that not telling you what it is?

-- 
Darren New, San Diego CA, USA (PST)
   People tell me I am the counter-example.

Post a reply to this message

On 2/1/2012 8:09, Francois Labreque wrote:
> I'm no Windows Server expert, so I don't know if it allows you to extend
> disk space on the fly, but I do know that many flavors of Unix do allow it.

It does.

-- 
Darren New, San Diego CA, USA (PST)
   People tell me I am the counter-example.

Post a reply to this message

On 01/02/2012 6:25 PM, andrel wrote:
> In short you have to choose: complain about your job or complain about
> all sorts of technologies that you were not aware of, but you can not do
> both.

I think that you are wrong, there. ;-)

-- 
Regards
     Stephen

Post a reply to this message

On 02/02/2012 02:50 AM, Darren New wrote:
> On 1/31/2012 1:12, Invisible wrote:
>> As usual with Wikipedia, the page babbles about updates and feeds and XML
>> and "syndication" and something about RDF, but utterly fails to
>> explain WHAT
>> IT IS.
>
> I have to ask... Do you start reading at the beginning of the article,
> or do you skip over the part that comes before the table of contents or
> something?
>
> First sentence in the article:
>
> "RSS ... is a family of ... formats used to publish frequently updated
> works ... in a standardized format."
>
> How is that not telling you what it is?

HTML is "a family of formats used to publish works [frequently updated 
or not] in a standardized format". As is PDF. As is PostScript. How is 
RSS different?

Sometimes the dictionary definition of what something is turns out not 
to be very enlightening. For example, you could say that

   "A knife is a device constructed from a hard material, usually in the 
shape of a triangular prism who's cross-section has a very acute angle 
between two of the sides."

Or you could say "a knife is a device for cutting things". The latter is 
infinitely more illuminating.

Post a reply to this message

>> I'm saying that if (for example) I read somewhere that a lot of
>> companies use Citrix to host their applications, that doesn't really
>> qualify me for a job managing Citrix. If I had actually /used/ Citrix,
>> or something vaguely like it, then yes. But having read about how it
>> exists and people use it? Not so much, no.
>
> Knowing about the trend, though, in the use of Citrix for telecommuting
> (for example) is something that's actually useful.  No, it doesn't
> qualify you to manage a Citrix system - but that's not the point.  The
> point is not looking like you're not aware of the trend when asked about
> it in an interview.
>
> Combine a demonstrated ability to quickly assimilate technologies with an
> awareness of what's going on with the industry, and that is something
> that looks good.
>
> But if you're unaware of what Citrix even *does*, then that calls into
> question (in an interview) whether you even know what's going on in IT.

I can see that knowing about how (say) Google manages their data centres 
might be quite useful if you're applying to Google. If you're applying 
to somebody who isn't Google, I'm not sure how that's useful.

...unless it *isn't* useful at all, it's just another one of those 
worthless things that "create the right impression".

>> As usual with Wikipedia, the page babbles about updates and feeds and
>> XML and "syndication" and something about RDF, but utterly fails to
>> explain WHAT IT IS.
>
> <sigh>
>
>  From wikipedia:
>
> --- snip ---
>
> RSS feeds benefit publishers by letting them syndicate content
> automatically.

WTF does "syndicate" mean?

> A standardized XML file format allows the information to
> be published once and viewed by many different programs.

Because XHTML isn't an XML format already. Oh, wait... actually yes it 
is. And many different programs can view it. So...?

> They benefit
> readers who want to subscribe to timely updates from favorite websites or
> to aggregate feeds from many sites into one place.

This at least hints at what RSS is actually about. But it still seems 
quite vague. I'm still not clear exactly what it's getting at.

> RSS feeds can be read using software called an "RSS reader", "feed
> reader", or "aggregator", which can be web-based, desktop-based, or
> mobile-device-based.

So... you need software that supports RSS in order to use RSS? OK, fair 
enough.

> The user subscribes to a feed by entering into the
> reader the feed's URI or by clicking a feed icon in a web browser that
> initiates the subscription process.

We still haven't established exactly what point "subscribing" serves, 
but OK...

> The RSS reader checks the user's
> subscribed feeds regularly for new work, downloads any updates that it
> finds, and provides a user interface to monitor and read the feeds.

This is all very abstract. It checks "regularly" for "new work", 
downloads any "updates", and provides a UI to "monitor" such updates. So 
what does that *mean*, in real world terms?

> RSS
> allows users to avoid manually inspecting all of the websites they are
> interested in, and instead subscribe to websites such that all new
> content is pushed onto their browsers when it becomes available.

As best as I can tell, the idea behind RSS seems to be that you can see 
if any of your subscribed websites have been updated, without having to 
visit each of them one at a time. (As if that's in some way "hard" or 
something.) Why the heck the article doesn't just /say/ this on line 
one, I don't know. Instead it talks obliquely about how "all new content 
is pushed onto the browser when it becomes available". (Funny, when it 
says a feed reader "regularly checks for updates", that sounds to me 
like a /pull/ model, not /push/...)

> Now, I read your blog and keep up on it by using - that's right - an RSS
> feed.

Damn... and I thought I'd turned that off... heh. Apparently not.

> I have the feed set up in Google Reader so that when you post
> something new on your blog, I see it as part of the Reader page.
>
> That way I don't have to visit your blog to see what's going on in your
> blog.  I see an item show up in my reading list so, as wikipedia says, I
> "avoid manually inspecting all of the websites [I] am interested in" and
> can see what's new.

So what does that actually look like? I'm still trying to get my head 
around how this actually works. What counts as "new content", how it 
displays all this stuff in an intelligible form, and so on.

>>>> I usually visit Tom's Hardware when I want to see what's happening in
>>>> the hardware world.
>>>
>>> I doubt you're going to get that by reading some text on a screen.
>>
>> That's why I just built a new PC - to experience the Core i7 first-hand.
>> :-P
>
> So then why bother going to Tom's Hardware again?

Sarcasm? :-P

>> The BBC's iPlayer system "works". I mean, it's so horrifyingly blurry
>> that you sometimes can't see people's faces clearly enough to recognise
>> who's who, and often the end credits are unreadable. But technically
>> that still counts as "works", right?
>
> I don't know what kind of connection you use, but I stream on iPlayer
> occasionally from halfway around the world (did that with last night of
> the proms IIRC) and projected it onto a 10' screen.  Didn't look
> particularly blurry to me.

Want to bet that the BBC has servers all over the world?

With the latest update to our set top box, we can actually access 
iPlayer and display it on a real TV. I can actually compare the recorded 
TV broadcast directly next to the iPlayer version of the exact same 
program. And let me tell you, the image quality is incomparable. (And 
that's only SD, not HD.)

On top of that, at peak times iPlayer becomes almost unusable. It 
freezes constantly. I'm not sure whether it's the BBC servers or the ISP 
network that can't keep up, but you just can't watch anything. But then, 
if you select "high quality mode", then it runs like that all the time.

I don't think an 8 Mbit/sec Internet connection would be considered 
especially slow...

>> I just looked it up. The transfer rate of a DVD is 10.5 mbit/sec. The
>> maximum broadband speed you can get is 8 mbit/sec. So... does that mean
>> that people in America have something faster than ADSL or something?
>
> I don't - I have 3 Mbps down ADSL.  I have to not be doing other things
> with the network connection when I'm streaming Netflix, but I do get a
> high quality HD image with 5.1 sound with programmes that include it.

The sound isn't the problem, it's the video. Sound is easily streamable. 
But I'm baffled as to how you can download video in anything approaching 
real-time, unless the quality is diabolically poor.

> But more to the point, do you now understand what streaming is?

Yes. Although I'm still puzzled as to how anybody could make money out 
of selling such poor quality stuff...

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