hard drives

[windog]

First thanks for all the comments on my oroposed spec - lots of food for thought.

Can somebody give me a numpties guide to hard drives, what is the benefit of SATA and RAID

One thing I want to do with my computer is use it to recieve digital TV, play it on the monitor and or tv screen and obviuosly use it as a recorder. I believe this may use up to 2 gig p/h and so even a 120 gig hard drive may fill up quite quickly.

Would I benefit from 2 hdd in the fullness of time and can I dedicate one of these to recording

Windog

[Austin]

Well basicly the first thing is the key interface. Current ones are ATA100, ATA133 and SATA150, SCSI is high end stuff and way expensive. The higher number the lower the CPU usage and the higher the theoretical bandwidth, but even 100MB/s (ATA100) is rarely limiting. ATA is also known as PATA (Parrallel ATA) whereas SATA (Serial ATA) is the new std but unlike the ATA133/100/66/33 it is not pin compatible (or even power compatible).

SATA has a few key benefits over PATA, firstly lower CPU usage and higher bandwidth but neither of those are truly significant for current drives. Next is the potential for hot swapping, plugging and unplugging drives while the power is on. Then there is the lower power draw and the better designed cables (small so don't inhibit airflow). PATA generally comes in the form of 2 connectors on your mobo, each able to handle 2 devices (HD, CD, DVD etc)with one as the Master and the other a Slave which is set by jumpers on the back of the drives (they share the cables bandwidth) ... SATA is dedicated to one drive and gives all the bandwidth, so no more sharing nor Master/Slave stuff. Finally (AFAIK) SATA drives tend to always be 7200rpm with 8MB and are generally slightly faster than their PATA counterparts. For most things the average user will do an ATA100 7200rpm 2MB HD is more than adequate.

This is all to the best of my knowledge so don't take it as 100% accurate.

[Austin]

RAID is where you typically use 2 or more HDs to speed things up, keep a constant backup or both. You need a specialist controller although this can be built into the mobo, not all controllers are equal but diffs aren't overly significant. You can use the following types of RAID:

RAID 0 (striping) = Uses your HDs together and splits files up into stripes and places them across multiple HDs. This makes writing and reading faster. The size is limited to the size of the smallest HD multiplied by the number of HDs in the array (collection of HDs). The speed is also dictated by the speed of the slowest HD in the array. That's the basics I won't get into stripe sizes.

RAID 1 (mirroring) = Writes identical data to each HD simultaneously so basicly keeps an imidiate and constant backup. If one is infected by a virus then so is th eother, it's a safe guard against drive failure more than anything else. This is not about speed but data safety, reading is sped up a little as data can be read from both HDs simultaneously. Again the smallest and slowest HD dictates the capacity and speed.

RAID 5 (both) = Stripes across 2 HDs (RAID1) while you can use 1 more HD to keep parity info. You can use the parity info to rebuild any one of the HDs should they fail. You actually constantly swap between which HD gets the parity data so no 1 HD actually stores only parity data. RAID 5 requires more hw support and is more expensive even before you get into actually buying the HDs. There is a small overhead in calculating the parity data so you don't get the same speed boost as RAID 0. The capacity is equal to the smallest HD multiplied by the number of HDs in the array minus 1 (for the parity). Again as for RAID 0 or 1 you should really get identical HDs.

RAID 10 (IIRC) = Tries to do RAID 1 + 0 which gives you 10. It tries to use 2 HDs to provide a speed boost whilst also keeping parity but from what I read some time ago it doesn't really work in practice.

The speed improvement with RAID isn't as remarkable as you may imagine. 15% is often as good as it gets IIRC but basicly you'll never achieve true double speed, in fact with a poor stripe size you can easily be slower than a single HD. The downsides of RAID are the added cost, more HDs means a higher chance that one will fail, more power draw, more heat inside your case, more noise (2+ HDs are louder than 1) and more difficulty in upgrading your HDs or mobo/RAID controller.

[TiG]

Originally posted by windog
First thanks for all the comments on my oroposed spec - lots of food for thought.

Can somebody give me a numpties guide to hard drives, what is the benefit of SATA and RAID

One thing I want to do with my computer is use it to recieve digital TV, play it on the monitor and or tv screen and obviuosly use it as a recorder. I believe this may use up to 2 gig p/h and so even a 120 gig hard drive may fill up quite quickly.

Would I benefit from 2 hdd in the fullness of time and can I dedicate one of these to recording

Windog

My personal experience of recording TV to computer is not particularly successful, i wasn't happy with the quality of recording, and i would have to suggest a specialist hardware box as the best way forward, something like the Sky plus box or TIVO is a good idea, Much more hardware support for the sort of things you are likely wanting to do.

In my opinion you would really want to look for a specialist TV card which is going to cost you a lot of your £500 budget if you really want to do something like this properly, the All in Wonder cards from the ATI range for example and upwards of £300.

I wouldn't suggest skimping on Graphics if you really want to do this properly.

Although Austin's descriptions of Raid are reasonably accurate, i'm sure it doesn't really help you in deciding stuff against your system. Really the only thing that would help you record TV to your machine is the Raid 0 stripped array.

You're 2 identical hard drives would act like one, theoretically doubling your write potential, providing processor/memory etc can feed data to the system quick enough. I've currently got this setup on my Pentium setup using ata133 to sata converters to try and see what difference it made.

The difference from ata133 to sata wasn't particularly noticable, a few % points and a lot less CPU usage when heavily accessing disks. But when i've stripped the disks into raid 0 its made a huge improvement in performance of my machine.

Future Sata drives will show huge improvements over current PATA technology, but we're a fair way from that.

Hope this helps some
TiG

[windog]

Thanks guys
So using Raid 0 I can efectively expand my hard drive capability to 240 or even 360 gig (using120 gig drives) to use for recording video. How many drives can you (or may it be sensible to) array together ?

Widog

[steve threlfall]

This wont be cheap tho mate..

[TiG]

Depends on the Raid controller, I can only stripe 2 on my current setup.

But at work we've got Ultra wide 320 scsi setup with 12 drives raided, Think it comes out at something like 600GB of space. Scsi is much better at handling larger disk arrays, and its why you spend more on them.

TiG

[TeePee]

Or what about RAID 15

A RAID 5 Array of pairs of mirrored drives..

Not to be confused with RAID 1.5 which I believe some Highpoint cards have.. I'm not sure how that works though...

[windog]

Thanks TiG

I wasn't really including this idea in my £500 budget, this is to add on when the next chunk of dosh comes available- i.e. where I am working towards, but obviously it influences my choice of kit in the first place

Were you using a digital or analogue decoder when you were not happy with the recording and how much do you think may have been signal quality in your area.

From what (limited!) understanding I have of the systems available the moment the hardware is "adequate" but the software is questionable if only that it is in its infancy.

Interested to know what you think

Windog

[windog]

Steve - no I realise this, but as I said in my prev post it is something to build towards (for me to save towards from what the wife allows me !) but to bear in mind when buying the original kit.

TeePee

Pardon ?

However - no I dont think it sounds likely to help ! Thanks

Windog

[TeePee]

THG has pretty pictures of RAID 15

http://www.tomshardware.com/storage/...aid_15-02.html

[Austin]

RAID 0 never gets close to doubling perf, IIRC you get very little true gains and can often get the same sort of gains by running 2 HDs seperately in a logical manner (one for Windows, one for swap file etc). That way you avoid the costs, headaches and increased risks of RAID. TiG was there anything partic in my RAID summary which was inaccurate or something I neglected, just so I can get it better next time it comes up?

Anyway I really suggest avoiding RAID unless you're absolutely sure it's for you. One of the std ATA100/133 HDs with 7200rpm and 8MB should be easily fast enough for even more extreme uses than you seem to need. 120GB isn't overly expensive, 160GB should be pretty reasonable too, you can easily add one later if you need more capacity but if you want RAID it's best to go for it from the off.

I would suggest you get a Digital TV PCI Card, it should only cost £80. This can recieve the 30 odd high quality digital channels so long as your aerial and area are up to receiving it (see link below). This way you can easily record as broadcast digital TV as it is already in MPEG2 format so it's a very simple process to stick it to HD. MPEG2 (aka SVCD) takes up about 700MB / 1xCD for around 50-60 minutes (IIRC) ... if this is unacceptibly large you can convert the final video into a better format like DivX / MPEG4 which allows you to fit 120mins of practically DVD quality video on 1xCD / 700MB. Of course you could get a DVD Writer to burn your finished stuff off, that way it doesn't have to be split into 700MB chunks so you can burn to a CD or alternatively sit on your HD the whole time. What sources would you be likely to use as an input (to record from)?

http://www.freeview.co.uk/whatson/index.html

[windog]

Thanks Austin
So I can use 2 hdd without RAID ? How does that work ?

I had considered a DVD writer as a future purchase but am I right in that there are two formats fighting it out at the moment ( as in vhs/betamax with videos past) or have I got that wrong

As far as recording sources TV and possibaly a digital camcorder in the future I think

As you can see from my questions what I am trying to do is put together the system now that I can add to in the future

Do you have any reccs as to TV card ?

Windog

[Austin]

Info on DVD ... http://forums.hexus.net/showthread.p...7311#post17311 . The 2 key formats are +R/RW and -R/RW but affordable burners (£130) are coming into the market which can use both. Still early days but if you need the capacity it's just about becoming a good time for consumers now.

Any mobo can connect up to 4 IDE devices (HD, CD, DVD etc). So you can easily stick in 2 HDs without the need for RAID. If you want to record from a digital camera just ensure the mobo has firewire (IEE1394) as many do, add-in cards are cheap anyway. I'm not up on digital cam corders but again they should use an MPEG2 type format so the processing uinvolved should be very minimal ... you only need to process the video stream for editing, re-encoding (to use a more efficient algorithm for good quality with a small file size) or when recording from analogue devices (like std TV, VCR, traditional camcorder). This is obviously to the best of my knowledge but should be pretty accurate.