Calculating the speed of harddisks (part 6)

What about Raid you might ask ?

Indeed, when you put a harddrive together with a couple of other drives, it
improves the performance. The best way, by far, is Raid. Some Raidlevels will give you better performance, while others improve security above all else.

Raid 0

Raid 0 is of course the most dangerous Raidset, and should be avoided in any situation where the data is critical. But when it comes to performance, it is the best there is. Multiply the speed of one disk, times the number of disks. If that number does not exceed the speed of your scsi bus, then you are smiling.

Raid 1 and 1+0

Raid 1 and 1+0 are often referred to as being the most expensive Raidsets. This is partly true, since you have to buy twice the number of HD's to get half the capacity. But they deliver outstanding performance.

consider this :

1 disk delivers 20MB/s. When configured in a mirror, the system is able to do "Split Seeks" which means that it can read from two disks at the same time. So 2 disks give you 40MB/s when reading. When writing, the speed will not go up, since everything has to be written twice. If your diskset performs 60 writes and 40 Reads, then you get 180 IO's. On a Raid 0 this would have been 100 IO's.. but on Raid 5, it would require 220 IO's -- I will clarify on a next installment. Cheers !

Calculating the speed of harddrives (part 5)

So, what about ATA disks. The thing with ATA disks, is that they are what they call "blocking" devices. This means, that only one disk per channel can communicate with the controller at the one time. Since most computers have two channels, two devices can talk to the controller. (SCSI is also referred to as "Non-Blocking device"). This is the reason why programs like Nero burning rom will recommend you to put your primary CD on one channel and your writer on a different channel.

An average ATA harddrive has a very good latency, but a rather high seek. This means that sequential transfers can be faster than on SCSI disks. But when you run a database on such a thing, it turns bad.
Secondly, ATA harddrives have a very low MTBF (Mean time between/before Failure), which means that the harddrive will not work for very long without critical errors. This is the reason why servers containing ATA harddrives usualy have only 1 year of waranty... and if it says 3 years, usualy this waranty does not include the Harddrive. But as long as you are running sequential transfers... ATA can a good solution. Don't burden your HD with a database though... certainly not on the harddrives used in portables, which have an even higher seek.

Cool Software for PocketPC

I installed DockWare on my Pocketpc, it turns my iPaq into a standing calendar… the freeware is nice, no nag-screens, but you have to start it manualy and it is not as configurable. Fun software, which makes your pocket pc next to your computer actualy serve a purpose.

PocketPCFreewares - DockWare

DockWare is a calendar/clock that you can use while your PPC is cradled. It allows you to use your pictures or drawings as a background and/or as a slide show.
There is a "Pro" version ($9.95) available allowing you to add a time interval to the picture rotation, to manage the text and background colors and to add a password option.

Calculating the speed of harddrives (part 4)

So, what can we conclude. SCSI is a nice thing, because the multitasking allows you to work with multiple harddrives at the same time. One harddrive is very fast, but not the speed of your SCSI bus. To get the most out of your SCSI bus, you need to combine multiple HD's e.g. with Raid. When you have an environment which is mostly sequential, then setting the blocksize higher than 64KB will give you very good performance. Combining 3 or 4 HD's will multiply the speed.

Random environments will need to take into account that the speed of the controller is not an issue when looking at the speed of your datatransfers. The speed of the harddrives is so low, that any controller can accomodate the transfer..

Calculating speed of harddrives (Part 3)

So, what about Random transfer ? As I mentioned earlier (Part 1), the speed of a harddrive depends on 2 factors : Average Latency and Average Seek. On an average SCSI harddrive, the Seek = 3 Milliseconds. But when you need to look for your data on a totally different place on the harddrive, both latency and seek need to be taken into account. So 6ms for each access to the HD in case of Random. 1 I/O takes 6ms, in 1 second, 1000/6 = 166 IO's/second. As I mentioned earlier, databases transfer small chunks of data lets say : 4KB. 166*4 = 664KB/s. you would need some 640 harddisks to reach the maximum speed of Ultra 4 SCSI.

Calculating speed of harddrives (Part 2)

So what does this add up to? When you want to know the speed, you need to know what data transfer type you are using. Sequential ? or Random ? An average fileserver and printservers use Sequential transfer, which occurs most when you transfer big files in one go. Database servers, like Oracle, SQL or Exchange, use Random transfer. They transfer small chunks of data (a zip code being updated, a mail message of 2KB being transferred.

In a sequential environment, only the Latency of the harddisk really counts. So lets imagine, we are going to transfer 64KB Blocks to a harddrive, with a Latency of 3 Milliseconds. The harddrive can have a maximum of 1 I/O (input or output) every 3 Milliseconds, so in 1 second, that is : 1000/3 = 333 IO's/second. 333 * 64KB = 21312 KB/s, which is equal to 20MB /s. This harddrive has a peak transfer rate of 20MB/s. You will need to attach 16 of them to reach 320MB/s (Ultra 4 SCSI).

Calculating speed of harddrives (Part 1)

How fast is a harddisk? Some people will answer the speed of the bus to which the harddrive is attached. Ultra ATA should give you some 133MB/s, Wide Ultra 4 or Ultra 320 SCSI should give you
320MB/s, but never in your life will you get that kind of speed from only one harddisk. So, what is the speed then.

To find this, you need to know two things about the harddisk :  Latency and Seek.

Latency is the speed at which any next spot on a track of the harddrive is brought to the head. This means, while the head remains passive, Latency is influenced by the rotational speed and determines the speed
with which the harddrive can read consecutive blocks of data. Usualy, SCSI and ATA harddrives score very well at this. Some ATA harddrives will even outperform SCSI harddrives at this.

Seek is the speed at which any spot on the harddrive can be located. Including data that is stored on a different track. This includes moving the head of the harddisk.
This is typically something at which SCSI harddrives are much better then ATA harddrives.

 

Nice Little bug in Business Objects 6 (end-user)

This bug has existed in BO v6 ever since it came out.

When starting a new report, from the data menu, select “New Data Provider”. The screen that now appears, has one radio button.

Why is this radio button here… it does not serve a purpose, since creating a query based on another one, implies that you already created one. If you check it, you cannot uncheck it.

The only thing that works is to click the Begin button.

RSS Feeds in Mozilla Firefox.

As I wrote earlier, in one of the articles on this blog, it is possible to put Live bookmarks on your buttonbar at the top of Firefox. But, this works easiest if you have the icon in the bottom right corner (see previous article). What to do however when you want to bookmark a site where you don’t have that icon, but only a hyperlink with an xml file at the end.

The solution is easy. Create a bookmark on a site where you do have an icon in the bottom right corner, then, in bookmark manager, change it’s properties to match the XML file on the site with interesting articles. Set a different title, and disco, you are done.

Example : ZDNET does not offer that icon; but when you first surf to theregister.co.uk, create a bookmark, change the properties of that bookmark to the url of ZDNET, then it works nice and dandy ;-)

Main differences between BO 5 and version 6.5 (client)

From the client’s point of view, the amount of differences available in BO 6 are not that big. That is, if we are talking about a basic user. Of course, a great addition, is the fact that you can now save your document to Excel. This includes Charts and tables on different reports. Existing reports are saved as Worksheets in your workbook.

A second addition, worth mentioning is the fact that you now have a search window in the Query Panel. When you work with big universes, this is no luxery. The same addition was introduced in the designer module.

So far for the basic stuff.

A cool new addition is the fact that you can now query webpages as well. This means, that you can select  a table on a webpage (e.g.:stock info on yahoo) and configure BO to query that page automatically. BO can then change the query automatically, based on the info required.

New in Business Objects XI Designer

Nice novelty in the Designer program of Version XI, is the possibility, to set rights
on the level of objects. To do this, you select the object, and click the icon on the toolbar… next, you choose the user for which you want to assign the rights. These objects will not show in case the user does not have the right.

Second new thing are the derived tables. You can actually create a table based on a sql query and use that as a datasource… quite useful.

 

Upgrading BO 5 to BO 6 (first installment)

Since my motto is : don’t believe it until you see it, I’m installing a BO 5.1. The purpose is to get it up and running, and then — for fun — upgrade it to BO 6.5.

To get me started, I first set up a VMWare session with W2K3, and put SQL 2000 on it. So far so good. The installation of BO 5 went quite nice. Now I wonder how the upgrade to version 6 will work out.

Keep you posted !

Firefox Live bookmarks

You probably already know Firefox … if not (get it here); I’m a great fan of that thing. Especially the live bookmarks. Here’s what they look like :

 

 

What happens is, that you get a very specific icon in the bottom right corner ()when you surf to a site with live bookmarking (zdnet, theregister, this blog and many more) . When you click this icon, it adds a live bookmark to your list of bookmarks… so far nothing special. But when you open the list of bookmarks (Bookmarks > Manage Bookmarks — I think that’s what it’s called.. I use the Dutch version) now scroll down to the location of your new bookmark and drag it to the toolbar at the top (as in the screenshot) The result is very nice… you see the new things on your favorite newssite immediately.

Differences between v5 and v6 of Business Objects

There is a lot of talk going on about the differences between BO 5 and BO 6 ... here is a list some are trivial.. others ... less trivial:
differences exist
-in rouding
-between values 0.00 and -0.00
-in the number of lines in a report
-in sort
-in complex calculations(filters,multicubes)
-in timestamp
-in headings
-in the option "refresh when opening document"

Er is nogal wat interesse naar de verschillen tussen BO 5 en BO 6... hier is een lijst. Sommigen zijn triviaal... anderen... minder triviaal :
verschillen bestaan bij
-afronding
-de waarde 0.00 en -0.00
-aantal lijnen op het rapport
-sort
-complexe berekeningen(filters,multicubes)
-timestamp
-hoofdingen
-de optie "refresh when opening document"


I'm getting more info on the exact nature of each difference of course.

Functions in Business Objects designer version 6 and version 5

I surfed the web over twice, but the different functions available in Business Objects Designer are little or totaly not documented .. and certainly not in BO itself. Of course, there is the help you can get from SQL language. But that leaves out a good number of things possible.

Finaly, I came across a nice one : Minisoft ODBC

Still looking for the correct syntax for the CASE WHEN THEN ELSE END thing… Microsoft has something