Raid-5 array seems slow...

[Arkangyl]

I just got 3x 2 TB Samsung F4's when the Egg had them for $95 each. Setup a RAID-5 array through my motherboard (EVGA p55 sli) and then ran Windows NTFS quick format on the array.

Seemed to be working fine, however HD Tune is showing average speeds of 50 MB/sec and that seems slow

While I'm at work I'm trying a re-format with NTFS and non-quick format so we'll see how that goes.

Any other suggestions though?

 

[drescherjm]

1. 3 drives for raid 5 is not the best choice. Always use 4 or more.
2. HD tune is reading too small a buffer by default (causing excessive seeks) extend the read size
3. Software raid under windows is never great. However intel does have the best fakeraid.

 

[john4200]

I suggest not using ICHR RAID for anything important.

 

[Arkangyl]

1. 3 drives for raid 5 is not the best choice. Always use 4 or more.
2. HD tune is reading too small a buffer by default (causing excessive seeks) extend the read size

Is there some performance jump at 4? I understand the basics about how R5 works besides a general speed boost as the number of drives increase, I don't see why 4v3 would be overly huge?

3. Software raid under windows is never great. However intel does have the best fakeraid.

I suggest not using ICHR RAID for anything important.

Also I thought Intel raid was hardware RAID? I set the array up via CTRL + i at POST, NOT in any sort of windows gui. How does this differ from using an Areca or Highpoint RAID card? (besides not having dedicated physical buffer RAM)

 

[drescherjm]

Intel raid is software raid for raid 5 or 6 since it does not have a dedicated on chip cache with a battery backup and uses the CPU for parity generation. For raid 0 or 1 you can call it hardware raid since there is no extra processing needed or cache. It may even mirror the data in the chipset for raid 1 instead of havining to send the data to each drive separately from the raid driver.

 

[Arkangyl]

Ahh, makes sense, thanks for the answer.

So am I really gaining much by running R5? It's starting to sound like half-hearted security and not much else, especially since I'm losing a drive...

 

[drescherjm]

So am I really gaining much by running R5?

The answer depends on the application and how much you value your uptime. Raid is no substitute for a backup. At home I am moving away from using raid 5 and using individual drives instead and only backing up what can not be lost. Since most of my data is from my HTPC and I can live without that football game from 2 years ago, I just backup the few GB of data I need and I have removed the raid. This also allows me to spin down drives that are not in use.

At work where I have 20 to 40 TB of data and need as near to 100% uptime as I can ( I easily achieve 99.9+% with linux software raid ) I do this with a combination of 10 to 15 raid 5 and 6 arrays for data and raid 1 for the kernel boot on these 5 to 10 systems . I also have a 2 drive tape autochanger and 100+ LTO2 tapes since I do not trust disk for long term backups.

 

[Arkangyl]

hmm, well, this is for a home media / file server basically. The array sits in my desktop which is on whenever I'm home with the goal of being a centralized local for my media to make streaming easier.

The hope with RAID-5 was a minor speed boost over JBOD and the parity data security so that if any one drive crapped out, I wouldn't be out a huge chunk of data. Granted this is nowhere near mission-critical, however it's in the "I'd be pissed enough to lose it that I'm willing to spend $ on some security".

 

[sub.mesa]

Intel raid is software raid for raid 5 or 6 since it does not have a dedicated on chip cache with a battery backup and uses the CPU for parity generation. For raid 0 or 1 you can call it hardware raid since there is no extra processing needed or cache. It may even mirror the data in the chipset for raid 1 instead of havining to send the data to each drive separately from the raid driver.

Intel ICHxR RAID controller is FakeRAID and fakeRAID means it is just a normal SATA controller without any true 'hardware RAID' support. The only difference between a bland SATA controller and FakeRAID, is that FakeRAID have firmware that allow booting. the firmware is like a mini read-only RAID driver that knows just enough to read a few kilobytes from the volume, until the real Windows-based drivers take over and do all the RAID work.

There is no hardware acceleration whatsoever; fakeraid is 100% software RAID once you started booting your OS. If you are writing to a mirror; it would send data to both disks through the controller. While real hardware RAID would receive one stream and internally sends it to the 2 disks. So fakeRAID is nothing different than software RAID, but using proprietary non-OS drivers instead.

For RAID0/1 there certainly is extra processing as Intel RAID drivers are the only ones which implemented write-back; which can corrupt your entire filesystem but allows achieving very high speeds; basically you write at RAM speed which can significantly add in casual desktop performance.

Most people seem to think RAID5 and RAID6 is very intensive due to their parity; this is not true! Parity is reaaaaaaaaaaaaally easy; XOR instruction is one of the easiest instructions for your CPU. Even old CPUs can do more than 2GB/s of XOR; and new ones may be able to go as high as 100GB/s. Basically this instruction is SO SIMPLE that it is only bottlenecked by the RAM speed.

What causes high CPU overhead is not the parity/XOR; but rather the splitting and combining of I/O request, necessary to write faster than say 5MB/s. For RAID5 writing fast on HDDs, it absolutely requires writeback and split&combine engine. The split and combined I/O requests take a lot of memory copies and that appears to be the biggest overhead the RAID5 driver requires.

Due to this writeback in RAM, there is the possibility of corruption on your NTFS filesystem; which if it affects metadata means you can lose large parts of the filesystem. NTFS' light journaling is made for HDD buffers; not for RAM writeback.

Concluding, i think Intel RAID drivers on Windows give you speed, but not reliability or data security; invest in good backups and you might be able to benefit from the best of both worlds.

 

[Arkangyl]

Thanks for that explanation.

Long story short I was messing around in Intel Raid Manager late last night and accidentally setup a raid-1 array with my boot drive & my old storage drive, thus semi-wiping all my data... working on the recovery now, should be fine but still

new plan is to have two of the 2 TB's in RAID-0, just fr a slight speed boost, and to use the other 2 TB as a manual mirror for various pieces of data (docs, pics, music, etc.)

I'd be tempted to get a good RAID card and a 4th drive and do quality RAID-5, but it just doesn't make any sense for me right now (I was only using 1.5 TB of total space before this attempted upgrade)