Aces High Bulletin Board
General Forums => Hardware and Software => Topic started by: Krusty on September 16, 2008, 12:45:56 PM
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So, RAID has increased performance with read times, and depending on the RAID setup with write times (or not). Some setups have redundancy (which appeals to me).
Assuming a RAID setup with redundancy or parity, some way of recovering if a HD goes bad, how many drives would one need? I know you can do it with as little as 3 (maybe even 2?) but you probably don't start getting the improved read/seek times until you have 4-5 drives, right?
Assuming you have a motherboard with 6 or 8 SATA 3.0 plugs, what if you have a SATA optical drive and then 5 RAID HDs? Will it think the CD-ROM is part of the RAID and cause problems, or are most systems smart enough to only use the hard drives?
I notice a lot of people go for multiple smaller drives (say 50GB x 5 drives). Is there an advantage to this, other than keeping costs down?
Can you mix drive sizes? Say you have 3x 50GB, and have a 120GB? Can that 120GB be part of the RAID? I would guess "no" but I don't know. Also, can you separate a HD from the RAID so that the RAID is "drive C:" and the 120GB is "Drive D:" ?
I've read a little about the RAID setup in general, been looking at a couple of webpages, but none of them answered these practical questions I had.
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RAID 1 would mirror two drives. RAID 5 requires 4 drives. Raid 5 will give you read speeds close to Raid 0.
For RAID 1: Increased read performance occurs when using a multi-threaded operating system that supports split seeks, very small performance reduction when writing. Array continues to operate so long as at least one drive is functioning.**
Ford RAID 5: Distributed parity requires all drives but one to be present to operate; drive failure requires replacement, but the array is not destroyed by a single drive failure. Upon drive failure, any subsequent reads can be calculated from the distributed parity such that the drive failure is masked from the end user. The array will have data loss in the event of a second drive failure and is vulnerable until the data that was on the failed drive is rebuilt onto a replacement drive.**
You can build an array with non-identical drives, however the array will assume the capacity and performance of the smallest and slowest drive. I.E a 80gb 5400 RPM and a 250gb 7200 RPM will be seen as 80gb and access times will suffer. No buddy does this really, unless the drives are fairly similar. Not sure if it causes problems. There is JBOD (Just a bunch of Drives) which can combine drives of different sizes to be seen as one drive as a combined capacity but provides no redundancy.
Or you could do a Nested RAID 0+1 etc:
When nesting RAID levels, a RAID type that provides redundancy is typically combined with RAID 0 to boost performance. With these configurations it is preferable to have RAID 0 on top and the redundant array at the bottom, because fewer disks then need to be regenerated when a disk fails. (Thus, RAID 1+0 is preferable to RAID 0+1 but the administrative advantages of "splitting the mirror" of RAID 1 would be lost. It should be noted, however, that the on disk layout of blocks for RAID 1+0 and RAID 0+1 setups are identical so these limitations are purely in the software).**
**Wikipedia
Personally, I use RAID 0 in my current setup for several reasons. When I originally built my current system I bought the hard drives at different times. I originally had 1 250gb Maxtor and almost a year later added an identical drive (was discontinued but got it open box cheap). I took the risk of data loss, but for important data I always had several back ups on DVD or on my web server. Currently I still have my RAID 0 array on the same drives but have added a single 500 Seagate as another backup option. I'm also experimenting using FreeNAS on my old box as a file server.
I recently did a HDtach on my Raid drives and my lone Seagate drive. I get about 105-107Mbps burst read (I think? or was it write, whichever) on my 2x250gb Maxtors and about 75Mbps on the Seagate. Access times were 14ms on the Maxtors and 12 on the Seagate. The Maxtors (alone) don't spec as high as the Seagate in access times and cache. Same RPM.
Raid does suck when you want to re/install Windows (XP yes, Vista?) as you'll need that ancient floppy drive to load the drivers for RAID.
***Also, I'm no where an expert on RAID and know the basics beyond 0/1. I'm sure there are there posters here that can fill in or correct me.
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Raid5 requires only 3 drives. A pair in striped 0 and one drive handling the parity.
Raid 0+1 or 1+0 requires 4 drives.
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This RAID 0+1 and 1+0 confuses me... I apparently didn't look too hard, as I haven't run across them yet. Have any links that describe what they do?
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I looked into this when I started to build my latest system Krusty and my conclusion was that within the realm of desktop systems RAID arrays become a money pit of aggravation with almost no return on investment. If you find out otherwise please let me know.
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I'm mostly thinking about load/seek times for game files (level loads, swapping, etc) but it could also apply to editing projects and video files I work with from time to time, as well.
My CPU/RAM/GPU is fairly decent, and I don't have anywhere near the delay my old PC had while changing levels in HL2, but I still have a bit of a delay. Also the preloading of textures in AH2 I'd like to speed up if I could. It's an I/O issue. My drive is a Sata 1.5 connected drive and much faster than my old IDE, but I wonder how I could speed this up a bit.
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Im afraid most of what I have to say on speed would foment anti-Microsoft rebellion from individuals that claim to know better. I would buy the fastest hard drive you can get your hands on (10000 rpm SATA II 3 Gb/s or SCSI if you can) and add more RAM. I doubt very much that any RAID system driven by 'onboard controllers' would give you much benefit but mostly lead to failed components and aggravation and I think anything properly designed for performance would be too costly. I dont have much experience with RAM drives but that is another possible alternative.
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My OLD system with SATA RAID and two WD Raptor 10,000 RPM 37 gig drives was very fast. That was an old Soltek board. My new Asus board has refused to allow me to set up RAID, and even though I have 4 times the RAM (it's nearly twice as fast as my older memory) and a much faster processor, not to mention a better video card with more and faster memory, it is NOT as fast as my old Soltek rig for AHII. I hope to one day have a full weekend to back everything up on both drives, and reload Windows 2000 Pro, setting up RAID in the process. This rig I have now should be a beast, but it is just decent.
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There is another possibility I would like more analysis of. This is a company that produces SSDs for desktop use and this is supposed to really speed up load times for applications under Vista and using ReadBoost (which I thought was of no use but...):
https://www.cenatek.com/product_page_rocket_drive_micro.php
And a free software RAMdisk to try:
http://www.mydigitallife.info/2007/05/27/free-ramdisk-for-windows-vista-xp-2000-and-2003-server/
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I kind of wanted to stay away from SSD after reading some of the comments on Intel's new line of drives (the other thread), and I only have 2 GB so I think dividing that up for a RAM drive might be detrimental overall.
I wonder if you could get a RAID for Intel SSDs? WOW that would be expensive in an ungodly way, but the data redundancy would be nice, and the super fast drive in RAID would be even faster, right?
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This RAID 0+1 and 1+0 confuses me... I apparently didn't look too hard, as I haven't run across them yet. Have any links that describe what they do?
Krusty, just imagine two RAID-0 (striped) pairs next to each other, as a mirrored pair of striped pairs. It costs more, since you have four drives involved, but you get both the performance increases of striping and the security of mirroring.
Here is a good two-page PDF primer on RAID from the Adaptec web site:
http://www.adaptec.com/NR/rdonlyres/84938C6A-1431-4C78-8E08-8DFA064A7F34/0/abc_RAID_LRes.pdf (http://www.adaptec.com/NR/rdonlyres/84938C6A-1431-4C78-8E08-8DFA064A7F34/0/abc_RAID_LRes.pdf)
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Okay, that explains it. Thanks.
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I've seen benchmarks of real-world performance for raid 1, raid 0, and raid 1+0...
Raid 1 on typical mobo controllers is quite a bit slower than single drive performance.
Raid 0 on the same controllers is up to 50% faster, but seek times are nearly identical and typical overall performance is maybe 20% improvement.
Raid 0+1 on the same mobo controller gets you about the same performance as a single drive.
The problem is that although with RAID 0+1 you have redundancy, you also have 4x the chance of a drive failing. So yes you're protected against a single drive failure, but there is a 4x chance that you'll see a drive failure in the first place.
Personally, after trying out fast single drives and RAID 0 setups, I go with a single drive plus a daily full-system RAID 5 backup using a second system on my LAN (I got lazy and bought an Infrant ReadyNAS+ and put 4 500GB drives in it). I could easily switch to my primary system using RAID 0 and keep the RAID 5 backup scheme, and get the best of both worlds - decent backups that don't care about the architecture of the primary drive system, and RAID 0 speeds. But I had a good year with regards to savings, so I had a little spare cash to throw at the problem. Most people will be just fine with a single drive in their primary rig, and a single backup drive either in the same or a different system on the LAN, using automated daily backups.
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Raid 1 on typical mobo controllers is quite a bit slower than single drive performance.
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For the typical mobo implementation of RAID-on-a-chip, you are right, sir. Especially for writes. It is not likely to have the smarts - or cache - to be able to write that 2nd copy to disk during a subsequent lull in system activity.
Obviously, it pays performance dividends if you throw more hardware (real RAID controller with battery-backed RAM) at the problem. ;)
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I run a 1+0 and HD tach reported almost a double improvement in read/write performance. The I/O feels snappy also.
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I'm looking at the Adaptec RAID 5405 (http://www.adaptec.com/en-US/products/Controllers/Hardware/sas/performance/SAS-5405/) controller for my next build. Anyone out there have any experience with it? It is at the low end of Adaptec's range of cards with their 1.2 GHz RAID chip, supports several RAID configurations, and has 256 Mb of write cache (battery optional).
TIA :salute
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If you get a MB that supports Intel's Matrix Storage Manager you can have raid 10, that's raid 1 and raid 0, on the same pair of HDs. That let's you put your OS and critical files on the mirrored partition and your games etc on the striped partition. With 320 gig HDs costing $60 it's cheap, safe, and fast.
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I'm looking at the Adaptec RAID 5405 (http://www.adaptec.com/en-US/products/Controllers/Hardware/sas/performance/SAS-5405/) controller for my next build. Anyone out there have any experience with it? It is at the low end of Adaptec's range of cards with their 1.2 GHz RAID chip, supports several RAID configurations, and has 256 Mb of write cache (battery optional).
TIA :salute
What exactly does the battery back-up do? I noticed the batteries are Lithium Ion meaning they're rechargeable and I wouldn't expect more than 5 years service life out of them. And since it's proprietary, Adaptec will gladly charge you $150 for something that should be about $50 (with the attached circuit board).
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Among the advantages of a RAID controller with its own processor and RAM cache is that the main system CPU can (possibly) go on its merry way doing other things after sending an I/O request to the sub-system on the controller.
A battery backup for the RAM cache ensures that in the event of an abnormal main system halt any data still in the cache which has not yet been written to disk will be preserved. And yeah, I agree that the price for the Adaptec battery is a rip-off.
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If you get a MB that supports Intel's Matrix Storage Manager you can have raid 10, that's raid 1 and raid 0, on the same pair of HDs. That let's you put your OS and critical files on the mirrored partition and your games etc on the striped partition. With 320 gig HDs costing $60 it's cheap, safe, and fast.
Sorry, but the Intel manual (PDF file) says that the minimum number of drives for a RAID10 volume is 4. More info here (http://download.intel.com/support/chipsets/imsm/sb/manual70.pdf) on page 12.
Here (http://support.intel.com/support/chipsets/imst/sb/cs-012525.htm) is Intel's description of RAID1 and RAID0 on two drives via "matrix raid." I think they are trying to slickly sell "RAID1 and RAID0 side-by-side" as though it were RAID10, which is not, strictly speaking, true.
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The drives are partitioned. One partition is the striped drive, the other is mirrored.
It may not be strictly Raid 10 but it's essentially RAID 10. What is Krusty looking
for that this doesn't provide?
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On a true RAID10 array, all the data is mirrored, so it's safe, and all the data is also striped, so it's relatively fast.
On the Intel "matrix raid" setup, only half of the data is being mirrored, and only half is striped. The half that is striped is not redundant. So long as you accept that, it's fine, I guess.