VERY slow raid 5 - why?

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gse1

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And on the discussion here, I have RAID-5 setup with 3 SATA disks running at this time. I've did some benchmarks and compared it to the single SAS drive setup and 2 disk RAID-0 SATA disks.
Just out of interest, how did you benchmark the disks, because sequential writes and random access writes are 2 different things.
 

proof

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And on the discussion here, I have RAID-5 setup with 3 SATA disks running at this time. I've did some benchmarks and compared it to the single SAS drive setup and 2 disk RAID-0 SATA disks.
Just out of interest, how did you benchmark the disks, because sequential writes and random access writes are 2 different things.

You just got burned by a "newbie"...
 

Gianti

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And on the discussion here, I have RAID-5 setup with 3 SATA disks running at this time. I've did some benchmarks and compared it to the single SAS drive setup and 2 disk RAID-0 SATA disks.
Just out of interest, how did you benchmark the disks, because sequential writes and random access writes are 2 different things.

Can't get into details but using server testing software, developed internally at the company I work for. Takes about 8 hours to run over 100 tests under variable conditions.

Moreover, to recreate the picture with a simpler set of results one of the publicly available software can be used such as "HD Tach" or "MDB95".

Unfortunatly, I don't have the numbers to share with you - I ran experiments for my own purpose to choose between setups for my own system and never took a record of exact numbers.
 

bga

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Actually storagereview showed that the latest Raptors (ADFD) outperform all the current top 15K SCSI drives in a single-user scenario (including gaming). Something to consider!
Interesting test. The first I have seen using high end SCSI drives in a workstation setting. I have seen lots of tests of SATA drives used in server settings, where they invarably gets badly beaten on higher loads. I assumed that would also be the case in a workstation setting. Something to consider, that SAS might not be the best solution for "money is no object" PC's.
 

gse1

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And on the discussion here, I have RAID-5 setup with 3 SATA disks running at this time. I've did some benchmarks and compared it to the single SAS drive setup and 2 disk RAID-0 SATA disks. The final results putting RAID-5 with 3 disks very close to the RAID-0 in terms of reads and about 10% slower in writes, single SAS drive lost to both, though it performace was close and impressive. RAIDs were tested on the Intel's ICH-8R and SAS benchmark was ran on the blade server (designing them... so have access to the server hardware).
Well it appears I have to eat my hat, please pass the salt. Either technology has moved on in the last 5 years or my memory fails me. I recall that my figures at the time were backed up by a similar test done independently by one of my colleagues. Oh well....

Next time I get chance (if I get chance) I'll have to look into doing some more tests.
 

pppjunk

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I have a Linux PC with Athlon 64, and nforce3 mobo. It has a RAID5 array of five 250GB drives giving a terabyte of reliable storage. 2 disks have died already with no data loss.

Anyway it is very fast ; the bottleneck is the PCI bus : I get 120 MB/s read and write. Some day I'll replace it with a smarter mobo which does not have the HDD controllers on the PCI bus.

It is also very fast on access time.

I hate the PCI bus since this mobo also has the Gb ethernet on the same PCI bus, so network file transfers are limited to about 50 MB/s since data has to pass twice on the PCI bus. It sucks.

Linux software RAID is very smart. It consistently outperforms low-end adapter cards and eats so-called "mobo RAID" (fake hardware RAID) for breakfast any day. Only an expensive RAID controller can beat it (the expensive ones, with onboard cache, and command queuing, are really fast ; the cheap ones are not worth the money).

When copying files in KDE's explorer I don't even get the progress bar for a measly 50-100 MB file...

As for the original poster's problem I believe it is probably due to the software RAID he uses being a lot less smarter than Linux's one. So he should use hard RAID 1 instead, or get a real adapter card.
 

Caintommy

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As for the original poster's problem I believe it is probably due to the software RAID he uses being a lot less smarter than Linux's one. So he should use hard RAID 1 instead, or get a real adapter card.
Nice to see I'm remembered ;)

I'm leaning towards going back to raid 0 and just implement automatic backups to the 3rd drive.
What's a good strategy for this backup then?
I could of course just backup my most important files and accept some loss of non essential stuff if/when the raid0 crashes.
But maybe there's a way to mirror the data, ghost or whatever it's called?

And thanks a lot for your help guys, I'm already feeling much better about the situation now that I understand it better.
 

proof

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Heres what you do;

Seagate 1TB HDD
Western Digital Raptor X 150
Western Digital Raptor X 150
Seagate Cheetah 36GB 15k Serial Attached SCSI
Seagate Cheetah 36GB 15k Serial Attached SCSI
Western Digital Raptor X 150
Western Digital Raptor X 150
Seagate 1TB HDD

Stripe the Raptors for programs.
Use the first SAS for you OS.
Use the second SAS for your paging file.
Put the 1TB HDD in RAID 5.
 

pppjunk

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Personnally since I have RAID there is no going back.

My storage RAID5 is :
- 1 Seagate PATA 300G (replaced a dead Maxtor)
- 1 Maxtor PATA 250G
- 3 Seagate SATA 250G

And my OS RAID1 is :
- 1 Seagate 160G PATA
- 1 Seagate 250G SATA

In the first two weeks after install, I went through two Maxtors which both died of the Maxtor+nforce syndrome (SATA Maxtors on nforce chipsets work for a week then randomly fail).

Since then (2 years) the oldest drive which was a Maxtor 250G PATA died of old age ; and one of the drives in the RAID1 failed (an IBM deskstar).

I lost no data. When the OS drive failed it booted from the mirror without a hitch. No reinstall. I just got a system message from the OS telling me "go buy another drive". Buy drive, plug it, add to array, it rebuilds itself. That's how I like it.

Anyway.

If you have important files (everyone does) you need RAID1. With 250GB hard disks at 60 euro the cost is lower than your time bothering to install all the crap again when your neat fast RAID0 burns.

I still have backups on USB hard disks. RAID protects against HDD death but not against my stupidity (deleting files), or computer theft, power supplies catching fire, etc.

So.

Decide how much storage you need for :
- important files => RAID1
- the rest (ie. your legally downloaded divx'es he heh)

Place the OS and everything important on a RAID1 array built from two drives. All the rest goes on separate hard drives, maybe even USB.

Note also that RAID1 is faster than RAID0 for mostly-read accesses since, IF the controller is smart, it can distribute reads evenly on both disks. So, RAID0 would only make sense for scratch space and when you need the ultimate in megabytes/second (like, if you do a lot of audio/video edits). Or, if your controller is not smart.

Unless you're like me with thousands of RAW files from a digital camera and all my CDs ripped losslessly to harddisk, you don't need RAID5...
 

proof

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eVGA 680i T1 Mobo. 2 WD Caviar 16MB 250GB SATAs. They are for gaming. My OS is on a 15k SCSI and my paging file is on another 15k SCSI. RAID1 or RAID0 for the WDs? I will only be putting games and office on them.
 

Fedor

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Like he said, use RAID1 for your important information. Since games and office can be re-installed, I wouldn't classify them as important, so you may consider going for the extra speed of RAID0. However, of course never save your docs on a RAID0, and dont save savegames on the RAID0 where possible as well.

However, RAID1 isn't a bad idea even for your scenario. Games and Office will mostly be read from, and in that department a good RAID controller will mean that RAID1 performance is very close to RAID0 (for reads). You need to weigh your own priorities - whats worth more to you, peace of mind or a little more performance? Note that if a drive from RAID0 dies you will need to replace the broken drive and in the time you do that you will need to reinstall everything, whilst with RAID1 it will continue functioning whilst you replace the drive. So, RAID1 = virtually no downtime, RAID0 = time lost and plenty of downtime.
 

Fedor

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Like I said, depends on the RAID controller. Even so, again like I already said, reads will be similar in speed but writes won't. If you're putting games and office on it though, just about the only real writing you'll be doing is when you install the games and office, hardly something to give up peace of mind for, imo (but those are my priorities, like I said you need to set yours).
 

Caintommy

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Well, as we all know, reinstalling sucks.

Isn't it possible to do an automatic ghost (if I understand that correctly) every week for example?

Then if a raid0 drive fails I go out and buy a new one. format the disk that survived and then ghost back all the data.
Or have I got it all wrong?

(note, I don't have a clue how to do all this ghosting but it sounds good :lol: )
 

Fedor

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Sure that will work, but obviously then you need 3 drives. I know you have them, so that solution works for you, but in Proof's example there was only two.

Although you need to remember:
2 x 250GB RAID0 = 500GB.
2 x 250GB RAID1 = 250GB.

So the third drive has to be bigger than the other two to back up your RAID0 data, or you need to only backup the important parts.
 

pppjunk

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Sure, you can do a ghost and stuff, but you need to boot from a special CD (you can't ghost a live system). It's so annoying that, in the end, you won't do it ;)

It's better to have a RAID1 and backup important stuff on a USB drive (like, your accounting, mail, and photos, not your OS).

That way if a drive dies, nothing happens ; and if your computer is stolen, flooded, burns or anything, you still have your USB drive safely stored away somewhere else.

The offices next to my house had a file server and another one for backup. They got visited. They stole all the computers, including the server and the backup server. All accounting data is lost... They should have spent an amount related to the value of the data to protect it, ie. use offsite backup...
 

SomeJoe7777

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Sure, you can do a ghost and stuff, but you need to boot from a special CD (you can't ghost a live system). It's so annoying that, in the end, you won't do it ;)
Checkout DriveImage XML from Runtime.

Can do hot images (i.e. image your C: drive while Windows is running), you can schedule it to do the image at a certain time through Windows scheduled tasks, and best of all, it's FREE. 8)

I'm currently using it on my home machines to image my C: drives every week. I'm actually going to be excited the day one of my C: drives dies and I get to restore from the latest backup, LOL. :mrgreen:
 

Caintommy

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Sure, you can do a ghost and stuff, but you need to boot from a special CD (you can't ghost a live system). It's so annoying that, in the end, you won't do it ;)
Checkout DriveImage XML from Runtime.

Can do hot images (i.e. image your C: drive while Windows is running), you can schedule it to do the image at a certain time through Windows scheduled tasks, and best of all, it's FREE. 8)

I'm currently using it on my home machines to image my C: drives every week. I'm actually going to be excited the day one of my C: drives dies and I get to restore from the latest backup, LOL. :mrgreen:

That sounds great!
Is the image the full size of the raid 0 or just as big as the data used?
 

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