No mention of SCSI in PC build guide?

[mapesdhs]

Dear Rob,

With respect to your excellent "How To Build A PC" guide (hard drive
section), just wondered, how come you don't mention SCSI at all?
SCSI is obviously expensive new, but 2nd-hand the technology is
dirt cheap, far more reliable than IDE, etc., and much faster. For
example, I obtained an LSI U320 PCIX card for 25 UKP and a 146GB
15000rpm U320 Fujitsu drive for 52 UKP (1 UKP = approx. $2 US). A
typical new price for a 146GB 15K U320 drive is around 350 to 450 UKP
($700 to $900) so it's pretty easy to grab some mega bargains.

I get access times typically 3X to 4X better than IDE/SATA drives
(around 3ms), and RAID speeds that are through the roof (not with
a PC, but my best result so far from 2nd-hand SCSI drives is almost
500MB/sec). Plus of course SCSI allows for many more devices per
channel than IDE, etc. Perfect for those who want the best performance
for video tasks, etc. Oh, my system is a Dell Precision 650 btw (dual-XEON
P4/2.66, 2GB RAM, 4 x 146GB 15K U320 SCSI, Radeon X1950 Pro gfx).

IDE/SATA makes more sense for raw capacity of course, but I thought
it might be worth mentioning SCSI in the future for those who want
reliability and speed. Even more useful, it's fairly easy to find 2nd-hand
SCSI drives that still have valid long-term end-user warranties (I found
several with warranties valid until 2010 and beyond), so if the disk becomes
faulty it can be replaced for free. I did this with a 146GB 10K Seagate
which I won on eBay; it was faulty, but still under warranty, which is
precisely why I bid on it, so I had it replaced by Seagate. 8)

I recently upgraded my brother's Athlon PC. Along with a new CPU, gfx,
etc., I replaced his 80GB IDE with a 146GB 15000rpm U320 Hitachi drive
(cost 58 UKP on eBay, ie. about $116 US), again using an LSI U320 card.
To say the drive speed is now faster would (ahem) be putting it mildly. ;)

Just a thought...

Cheers! :)

Ian.

PS. Thanks muchos for your info in the CPU cooler section! I too have
been meddling with an Athlon64 3400+. 50C idle temp = ouch!! This is
with a new Thermaltake TR2-M6 SE(K8) heat sink and fan. Looks like
I need an extra case fan and the Arctic compound you mention. While
running Sandra Lite, at one point the temp peaked at 75C. 8|

[Rob]

Hi, Ian:

Very interesting. Thanks for mentioning this.

[mapesdhs]

Hi, Ian:

Very interesting. Thanks for mentioning this.

Most welcome! For reference, this is the disk auction I
won which I've put into my brother's PC (motherboard is
an Asrok K8Upgrade-1689, WinXP installed just fine):

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=200076901617

A quick check shows the normal new price for this model is
about 430 UKP atm (eg. uk.insight.com has it for 434.74 UKP),
while the best fixed 2nd-user price I could find was 260 UKP,
ie. my eBay win was one hell of a fast drive at a bargain price.

Btw, I think your article mentioned cache buffer size matters
somewhat. This disk (like most U320 15Ks) has 16MB cache,
average seek time 3.3ms, average latency of just 2ms, and a
sustained transfer rate of 93MB/sec.

And these are the three Fujitsu drives I obtained which I
put into my Dell system as an internal RAID:

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=250055376642
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=250055377201
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=250055375049

ie. I obtained about $2700-worth of SCSI storage for only
about $350 equivalent. 8) EDIT: just ran Sandra filesystem test,
I get 152MB/sec, random access time 1msec; the best random
access time of the comparison SATA RAIDs listed was 8msec,
with most SATA RAIDs giving 10 to 12msec.

I should imagine such drives are even cheaper on eBay USA...
holy grud, talk about bargainville! See:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=130088490816

$67! That's almost half what I bought mine for. :D Stuff 12 of those
in a JBOD case and... *drool*

Perhaps also worth pointing out that once one has an internal
SCSI controller available, using other related devices such
as a SCSI CDRW has further advantages, ie. main CPU not
involved in controlling the device, so CD burning is more
reliable (better multitasking).

SCSI is a bit of a learning curve, not for everyone, but for anyone
after a bit of quality, reliabilty and that extra speed edge,
some careful buying can result in some amazing bargains.

I hear the term 'prosumer' sometimes, ie. something
inbetween an ordinary consumer and a professional, which
is kinda what I'm getting at I guess. There's such a huge
surplus of 2nd-hand SCSI stuff on the market now, it means
the average joe can take a typical PC and fit it out with what
would normally be considered professional storage.

Cheers! :)

Ian.

[DemonicDerek]

What is a SCSI Hard Drive?

[mapesdhs]

What is a SCSI Hard Drive?

SCSI, which stands for Small Computer Systems Interface, is
a technology for connecting peripherals to a computer using
a standard set of communication signals and protocols. It
is most commonly used for connecting storage devices
(hard disks) but is also used for other devices (scanners,
tape drives, CDROM/CDRW, etc.) and some operating systems
can even use a SCSI bus like an ultra-fast network connection.

The technology used inside any hard drive (ie. the physical
storage medium itself, the magnetic material, etc.) is pretty
much the same, be it IDE, SATA, SCSI, etc., though SCSI
drives generally use better quality parts and are better
designed.

If I may quote Gary Field field from the SCSI FAQ at:

http://www.scsifaq.org/scsifaq.html

he says (though bare in mind he's thinking of the typical
high price of new SCSI drives here):

"For someone to who doesn't need a real multi-tasking workstation
or server, the only reason for paying the extra money for SCSI is
flexibility. EIDE/ATA is strictly for "inside the case"
peripherals. SCSI allows you to attach a large collection of
add-ons like scanners, CD recorders, tape drives (or even devices
not conceived of yet), either inside or outside the CPU case in
whatever manner suits your needs or wishes.

If you like non-technical analogies:

SCSI is like a palace, with an architecture that was well thought
out from the beginning and built upon over a period of time to
make it even greater than originally envisioned.

IDE/ATA is like a log cabin, with a dirt floor, built from
whatever was found lying around in late Fall just before the snow
came. It can't be expanded because it has no foundation and would
collapse under its own weight.

Both provide shelter. SCSI costs more (but not as much as a palace. :-)).

Take your pick."

Apart from individual peripherals like scanners and tape
drives, the most common use of SCSI is for highly scalable
data storage, ie. lots of drives in one unit all linked together,
for combined storage, better speed, backup solutions, or a
combination of these things, eg. I have a test setup consisting
of 36 x 73GB drives, all combined into a single 2600GB unit,
which I'm using for researching high-bandwidth solutions for
high-definition video editing (430MB/sec, my best result so
far, using 3 x U160 SCSI controllers. Will try with 6 controllers
when I have some time to spare, hope to go way over half
a GB/sec).


The main differences between consumer-level drives
(IDE/SATA) and SCSI are:

- SCSI drives bought new are much more expensive per
GB than IDE/SATA, though the differences vanish if one
compares the best SATA drives to good 2nd-hand SCSI.

- SCSI drives have extra circuitry to control how the drive
operates, the sending/receiving of data, etc. By contrast,
it is the main CPU that controls much of the operation of
an IDE drive. With SCSI, the main CPU is free to do other
tasks, which means that complex multitasking is far more
reliable, stable, etc. In other words, SCSI drives can cope
very well when multiple processes are trying to access
data at the same time, whereas IDE drives perform badly
under such conditions.

- SCSI uses a communications protocol that allows for many
more devices on a single channel (up to 15). This isn't
necessary for typical consumer systems, but gaming freaks
and any home user who wants to go that one step further
can do much more with SCSI technology, eg. highly scalable
RAID systems, very high bandwidth, very fast access times,
etc. It is ideal for small business aswell, eg. better reliability,
much faster database searching, etc.

- The quality of parts used in SCSI drives is better as they
are designed to be able to cope with intensive workloads
running 24/7, eg. video RAID, databases, large file systems
for multi-user networks, etc. Warranty periods are also
generally longer for SCSI drives (5 years). For someone
starting up a home bussines, where the system disk will
contain important data, using SCSI would mean better
reliability.

- The SCSI standard allows one to use cable lengths of up
to 12m, giving great flexibility for positioning equipment,
eg. a disk storage unit can be in a different room. I know
someone who has their SCSI video RAID in their attic. :D

- SCSI is largely backwards compatible, so even if one has
an older SCSI adapter card that is slow by current standards
(eg. FastWide, 20MB/sec), one can still connect modern
devices to the card, ie. a newer device will simply run at
the older slower speed automatically. Older devices can
also be connected to modern SCSI cards.

The vast majority of home consumers would not need what
SCSI has to offer, but because of the insanely low prices of
2nd-hand parts (especially from eBay) using SCSI instead of
IDE/SATA is one way of enhancing a system's flexibility, and
also making it faster and more reliable.

Something that has changed recently is that one can now
get the best of both worlds by using storage units which are
connected to the computer using SCSI, but the disks inside
the unit are good-quality SATA (eg. 10000rpm). The unit
includes circuitry to convert between SCSI and SATA; thus,
the end user gets the speed they want, but the price is much
less; there is still a reliability tradeoff, but the use of 'mirrored'
RAID setups makes this less of an issue.

Note that there are also Fibre Channel (FC) drives which are
another step above SCSI in scalability and speed; FC is a
storage technology and data communications standard that
allows for incredibly large file systems, massive data
bandwidths (the highest I've come across is 40GB/sec), and
the ability to use fibre optic cables for long-distance linkups,
faster speed, etc. FC supports 256 devices per channel and
allows multiple systems to access the same device at the
same time - it has elements in common with the way a
network operates. FC disks cost a fortune, partly because
they have a huge amount of memory included (typically 70MB).
But I digress, FC is beyond the scope of my post here. Sorry
Rob, was on a bit of a roll there I think... :)

For further reading, please see:

http://www.scsi-planet.com/

Cheers! :)

Ian.

[scs100303]

This is the first i've heard about SCSI hdd's (im a newbie), although i have done tons of research, all of which suggest the use of SATA type hdd's. So my question is why isn't SCSI more talked about and publicized online? And if its so amazing why is it sooooo sooo cheap on ebay compared to its SATA counterparts. Is this like an underground pc secret or what? Explain that to me if you can Ian. Thanks for all the info too:)

[scs100303]

this article says sata is faster?

http://www.pugetsystems.com/articles.php?id=19

[DemonicDerek]

Sata can be faster however it may cost a little more.

[mapesdhs]

scs100303 writes:
> This is the first i've heard about SCSI hdd's (im a newbie), although
> i have done tons of research, all of which suggest the use of SATA
> type hdd's. So my question is why isn't SCSI more talked about and
> publicized online? ...

Because without question as a technolgy to buy new it is not
appropriate for home consumer use. Most people simply don't need
the speed and scalability that is possible with SCSI.

I only mention it purely because 2nd-hand prices are so low, thus
making it so affordable for any hobbyist who wants to go that bit
further.


> ... And if its so amazing why is it sooooo sooo cheap
> on ebay compared to its SATA counterparts. ...

Because commercial users don't buy 2nd-hand in the same way
home/hobbyists do, so the nature of the 2nd-hand market is
different.

Most people want storage space, not speed, and certainly not
scalability. Much of the time, it is the OS or other aspects of
system hardware that limit what is possible in an overall system.


> ... Is this like an
> underground pc secret or what? Explain that to me if you can Ian.

No secret, just different commercial worlds.

In the 2nd-hand market, an item is only ever worth what someone is
willing to pay, ie. an item does not have any objective value when it
is sold 2nd-hand.

Thus, despite higher reliability, someone pay perceive a 36GB SCSI drive
as being worth less than an 80GB IDE because of the different storage
capacities. My own personal use of storage means I am more interested
in scalability, reliability and overall speed, so for me SCSI is more
interesting and more useful.


> Thanks for all the info too

Most welcome!


> this article says sata is faster?
>
> http://www.pugetsystems.com/articles.php?id=19

In a way it's a bit of a wierd article, eg. the same Raptor giving
different results in different systems - one should ask why. Plus,
what SCSI controller was used? That can make a big difference. Also,
the article doesn't say what the low level parameters of the SCSI
disk are - these may be important, especially if write caching has
been turned off by default. One can alter SCSI drive parameters to
optimise for one's application.

It's not hard to show some benchmarks where a modern 10K SATA disk
will be faster, though SATA drives still cannot match the access
times of SCSI. When I ran the Sandra suite on my SCSI RAID (3 x 146GB
15k) it gave an access time of just 1ms - far faster than any example
comparison SATA RAID mentioned by the Sandra test. However, the
articles' tests say nothing about the differing build quality levels
of the technology used with SCS vs. SATA, reliability levels, etc.
SCSI is designed to be able to cope with 24/7 use, IDE is not, and I
doubt SATA is built to the same standards as SCSI.

The article also doesn't cover the point that since SCSI storage
means overhead processing is not done by the main CPU, one can do
other things at the same time. Running multiple I/O intensive tasks
on a system with IDE/SATA is risky at best, especially if anything is
being done such as writing a CD, etc. For home users this isn't much
of an issue, but for hobbyist users who want to push the edge, it's
something to consider.

But like I say, it depends what you want to use a system for. If you
only want a single disk, a good 2nd-hand SCSI disk is an interesting
alternative to SATA, but not necessarily the right answer. If you're
the kind of hobbyist user who has tons of mp3 downloads, movies,
games dumped to disk, etc., then SATA is more sensible, but if you're
someone who wants to explore uncompressed video editing, then
2nd-hand SCSI is a good solution.

Btw, I just finished my latest SCSI RAID performance tests. So far
I can get 511MB/sec, a speed far beyond anything SATA can offer,
and I'm not done yet. :) Am hoping to break past 600MB/sec. To be
fair though, I use old SGIs for my storage processing - pretty hard
to get a PC going that fast anyway, though I've heard of a maxed-out
dual Opteron Linux PC pushing 480MB/sec.

Cheers! :)

Ian.

[DemonicDerek]

I thought that newer SATA hard drives can transfer data at 3 GB/s or so I heard.

On another note, since you know so much about SCSI then why don't you just write the section on SCSI for Rob and he could possibly add it to his book and site.

[mapesdhs]

DemonicDerek writes:
> I thought that newer SATA hard drives can transfer data
> at 3 GB/s or so I heard.

That is 3Gbit/sec, not 3GBbytes/sec, ie. 3Gbit = 384MB/sec.
Not that much faster than U320 SCSI really. Plus, this is the
max physical interface/bus speed, not an indication of the
drive's expected maximum sustained performance. There's
a world of difference between the rate at which the physical
drive media can transfer data and the maximum speed that
the bus connection is designed to support. Even SCSI disks
show this all too well, eg. the Maxtor Atlas 15K II disks I use
are U320 (max bus speed 320MB/sec) but the typical
sustained transfer rate from one drive is around 98MB/sec,
which for a single disk of any kind is pretty good.

Some SCSI disks can push 147MB/sec for a single drive (I
think there's a Fujitsu that can do this), but there isn't any
drive that can offer a sustained bandwidth even 60% of the
peak U320 bus speed. The same applies to SATA technology.

Indeed, if you have a look at a typical SATA drive of the
type you're referring to (in this case a WD RE2 500GB):

http://www.westerndigital.com/en/products/Products.asp?DriveID=238

the interface is listed as 3Gbit/sec as you say (which sounds
better than 384MB/sec - isn't marketing marvelous?), but the
maximum sustained drive transfer rate is only 70MB/sec. I
also note the RPM is just 7200 and the access time is around
40% slower than modern SCSI. However, the 3Gbit/sec bus
speed of these drives is obviously useful because you can
link them together in a RAID, thus getting much faster
combined speed.

An even better example of how not to be fooled by marketing
numbers is shown by looking at the WD 10K SATA:

http://www.westerndigital.com/en/products/Products.asp?DriveID=189

This drive has a bus connection only half as fast (150MB/sec),
but it is a faster drive with better performance (84MB/sec
sustained) and, due to its faster RPM, an access time more
akin to SCSI drives (2.99ms). But 10K SATA drives are much
more expensive, eg. in the UK a new WD 10K SATA 150GB
disk of the above type is 147 UKP (www.scan.co.uk) but I
can get a 2nd-hand 147GB 15000rpm SCSI for half that
price, and this is the point of my initial post: anyone who
really wants that kind of speed can get 2nd-hand SCSI at
better prices than new 10K SATA, yet still obtain better
performance, with added scalability, etc. which SATA doesn't
offer.

One might ask what about 2nd-hand 10K SATA? Sadly, such
drives are extremely rare, eg. right now there's not a single
10K SATA drive on eBay UK. There's a 74GB 10K SATA in Italy
(item 300097269754), but it's 95 UKP!! :D (about $200 US)
One can get 147GB 15K SCSI disks off eBay for less than that.
Similarly, there is only _one_ 10K SATA drive on eBay USA just
now, namely a 36GB 10K for $99 (I've bought 147GB 15K SCSI
drives for not much more). It seems the really fast SATA drives
barely exist in the 2nd-hand market. The drives sold to home
consumers are all 7200rpm.

But SCSI is, as described earlier, a scalable technology,
ie. one can have up to 15 drives on the same bus, so
it is logical to use a communications protocol that can
be much faster than any single drive. Plus, a system can
them combine multiple SCSI buses into a much larger
overall storage link. The tests I've been running use a
system with six U160 controllers (3 x QLA12160 SCSI
cards). I'd use U320 if I could, but the system in question
(a dual-600MHz SGI Octane2) is too old to support U320
(dates from 2000). I've been asked to setup a storage
array suitable for supporting uncompressed high definition
video; it's been kinda fun seeing just how far I can push
the technology. :D


> On another note, since you know so much about SCSI
> then why don't you just write the section on SCSI for Rob
> and he could possibly add it to his book and site.

Hmm, possibly, but would Rob want that kind of information
to be included? I guess it depends on his target audience.

Cheers! :)

Ian.

PS. Another point to remember: whatever a disk may physically
be capable of, it's also important whether or not the OS and
the application being used can cope with such high speeds.
Windows definitely isn't as good for such things as Linux,
but sometimes one may not have a choice.

[scs100303]

Thanks for the follow up:) You defiantly should write a guide of some sorts for Rob.

My only problem being new to pc building, is that SATA seems a lot easier to use. From what i've read SCSI can be tricky to get working. I'd like to try out SCSI (seein as i'll be doing HD video editing) but seeing as im not an expert by any means, could you tell me exactly how easy it is to use?

[DemonicDerek]

Hey, I'll be doing Video editing too but I am using SATA hard drives for the computer I am going to build. I am taking 2 500gb and raid 0ing em!

[mapesdhs]

scs100303 writes:
> Thanks for the follow up:) ...

Most welcome!


> You defiantly should write a guide of some sorts for Rob.

Heh, well, I'll leave it for Rob to ask if he thinks such a thing
is appropriate. ;)


> My only problem being new to pc building, is that SATA
> seems a lot easier to use. ...

Ach, SCSI's not that difficult really. It does mean learning
a bit more about the technology you're using, but then
again as I said before I figure the suitable target audience
would be those who want to get that bit more out of
technology, learn about it, etc.


> ... From what i've read SCSI can be tricky to get working.

It helps if you're using an up-to-date OS, eg. XP Pro. That
way, drivers for many SCSI cards are already included.


> I'd like to try out SCSI (seein as i'll be doing HD video editing)

You will be doing HD editing? As in 1920x1080
uncompressed? What software will you be using?


> ... but seeing as im not an expert by any means, could you
> tell me exactly how easy it is to use?

Assuming one learns a bit about it beforehand, pretty easy
IMO. For example, install a SCSI card, bootup and install
the drivers, power off and connect the SCSI disk with a suitable
SCSI cable, and with whatever jumpers set that are appropriate,
and that should be it. Note that SCSI cards usually have their
own configuration BIOS one can go into to set up other things,
and during startup one can see the SCSI card scanning for
devices, so bootup takes a little longer.

Your situation is a good example actually, assuming you
want to use uncompressed video. A 2-disk SATA RAID is
not fast enough for uncompressed HD, not by a long way,
whereas SCSI's scalability means one can obtain the required
speeds no problem vis using multiple drives. But you should
look into what is required carefully before buying anything.

Cheers! :)

Ian.

[mapesdhs]

DemonicDerek writes:
> Hey, I'll be doing Video editing too but I am using SATA hard
> drives for the computer I am going to build. I am taking 2
> 500gb and raid 0ing em!

If you're only editing PAL or NTSC video, even uncompressed,
then a SATA RAID of that kind should be more than fast
enough. High-quality uncompressed PAL only needs around
42MB/sec sustained, so in theory even a single modern drive
is fast enough (though a RAID makes things more reliable);
uncompressed NTSC needs a bit less, about 36MB/sec (these
figures are for high-quality professional standard 4:4:4:4; the
requirements are about half a much for a consumer level of
quality, ie. 4:2:2).

Many PC video editing solutions use some kind of compression
format though (eg. JPEG/MPEG), which requires even less speed.

Your SATA setup should work fine. No need for SCSI there
unless you want much better scalability in storage space,
eg. the external 12-bay units I use could in theory hold up
to 3600GB using 12 x 300GB disks, and one can get storage
units with much more than 12 bays if required (or link
multiple units together). If your editing involves any kind of
compression though, then you don't need such a large
amount of space. Even with uncompressed PAL/NTSC, the
2-disk SATA RAID you're going to use would have enough
space to hold more than 8 hours of material which should be
plenty (with JPEG compression, more like 40 hours).

And of course, once a video sequence is finished, if you
convert it to DivX/MPEG4 (whatever) it will shrink right down
even more. I use SGI machines for video capture/editing and
then PCs for the final conversion to DivX.

Are you using a particular dedicated video capture/editing
card using the software supplied with the card? What model?
Or are you doing it in some other way, eg. video obtained
via capture using the card, but edited with Premiere or
something?

Cheers! :)

Ian.