[SOLVED] RAID Controller

theking2 · 2014-01-02 11:27:46

Hi! I'm looking to upgrade my Archlinux drive file, media, backup server with a harware RAID5 controller. Sofar I've been doing softraid in a Promise PDC40718. Wich works but not amazingly fast. The hardware compatibility list does not sport storage controllers.

Is there a list of compatible or preferred controllers around?

Last edited by theking2 (2015-01-03 13:23:11)

Lone_Wolf · 2014-01-02 12:32:16

http://linuxmafia.com/faq/Hardware/sata.html , it's old but should give you an idea of what to look for.

The easiest way to find a good linux HW raid controller (Fake Raid tends have a worse price/performance ratio then sw raid)
is to look for enterprise class raid cards that have in-kernel drivers.

Apart from 3ware & adaptec, server manufacturers like HP and Dell sell hw raid cards.
Many server moherboards have on-board hw raid as an option, some names are supermicro and tyan.

Keep in mind that these cards are likely to cost 400 USD or more.
You will also want a battery backup or UPS solution for the card so you can use write-back/delayed writes without fearing data loss on power failure.
(if you plan to disable write-back imo you loose the biggest advantage hw raid has and should stick to sw raid)

Last edited by Lone_Wolf (2014-01-02 12:39:22)

theking2 · 2014-01-03 13:02:29

Thanks!
That is a good answer. I was expecting that price range for a controller but if there is a motherboard with build in RAID5 dual 1G eth. and kernel support it would be even better.

Will be checking out the tyan board. I do have a asus with maxtor controller for my workstation, but this is more a general purpose board. I won't need sound and only limited graphic support in a server, but it should do a fast network and storage. Currently I get a ave. 22MB/s upload from my current setup (over a 1G net). Which is fine but not very exciting. And I'm not sure what the bottleneck is.

R00KIE · 2014-01-04 14:55:23

You might have a slow cpu, one of the disks is slower or the controller you are using is causing trouble.

I would go with software raid5 (not fakeraid), most cpus should be fast enough to handle it without problems. One thing that Lone_Wolf didn't mention, and that you will probably see quite often is data recovery related, if you use software raid you can happily move the disks to any other computer and you know it will work.

Here's some tidbits I gathered from machines I have access to:

Machine with Core i7 870, 3x SAMSUNG HD103SJ, Gigabyte P55-US3L board, using software raid5:
kernel:
2.6.18-371.3.1.el5
from dmesg:
raid5: using function: generic_sse (12336.000 MB/sec)
hdparm result when reading from raid array:
Timing buffered disk reads: 500 MB in 3.00 seconds = 166.39 MB/sec

Machine with Core2 Quad 2.40G, 4x SAMSUNG HD250HJ, Gigabyte P35-DS3P board, using software raid5:
kernel:
2.6.20-2925.9.fc7xen
from dmesg:
raid5: using function: pIII_sse (1806.000 MB/sec)
hdparm result when reading from raid array:
Timing buffered disk reads: 642 MB in 3.00 seconds = 213.80 MB/sec

As you can see both machines are as common as you can get, both using normal sata disks and software raid5 and both are quite fast, more than enough to saturate even a 1Gb/s link (assuming you have big contiguous files to read from).

Lone_Wolf · 2014-01-04 17:30:08

Rookie is correct about potential data recovery issues with HW raid.

I've had to deal with problem servers using HW raid a few times.
one time the controller was failing, but the server still worked.
I inquired with the supplier of the card, they informed me that card was end-of-life since 3 years and they didn't have it anymore.
The controller manufacturer confirmed it was EOL and no compatible controller was available from them.

The raid drives themselves were fine, but the data was no longer accessible without a working controller.
Backup was over 6 months old, so not very useful (that server was not maintained by me or IT).
We ended up buying the card on ebay, for about double the original cost.

In short, if you go HW raid make sure you got a good backup solution running.

theking2 · 2014-01-12 12:25:21

Thank you Lone-Wolf and R00kie.

From hdparm I got

 hdparm -Tt /dev/md127

/dev/md127:
 Timing cached reads:   1124 MB in  2.00 seconds = 561.56 MB/sec
 Timing buffered disk reads: 318 MB in  3.00 seconds = 105.99 MB/sec

dmesg:

prefetch64-sse:  3985.200 MB/sec

Intel 945GCLF2 (Atom330 Dual)
with PDC40718 controller
and 3* WDC WD10EADS-00P8B0, and 1* WDC WD1003FBYX-01Y7B1 Western Digital HD.

so that is actually quit ok? Hardware RAID5 would not help me there? The other day I had to replace a failing disk (1TB). A rebuild on a new disk cost about 10hrs. In those ten hours I was holding my breath for another disk to fail.

Btw I understand (and teach my students :-) ) that RAID5 is not a replacement for backup.

Last edited by theking2 (2014-01-12 12:41:31)

R00KIE · 2014-01-12 16:54:02

I suspect you would do better with a different controller card [1][2].

As for read speeds I guess you should see around (n-1)*speed of slowest drive, where n is the number of drives in the array (if there are no cpu limitations or a bottleneck somewhere along the data path).

[1] http://www.aisecure.net/2011/07/07/prom … a300-junk/
[2] http://www.freebsd.org/cgi/query-pr.cgi?pr=116935&cat=

Arch Linux

#1 2014-01-02 11:27:46

[SOLVED] RAID Controller

#2 2014-01-02 12:32:16

Re: [SOLVED] RAID Controller

#3 2014-01-03 13:02:29

Re: [SOLVED] RAID Controller

#4 2014-01-04 14:55:23

Re: [SOLVED] RAID Controller

#5 2014-01-04 17:30:08

Re: [SOLVED] RAID Controller

#6 2014-01-12 12:25:21

Re: [SOLVED] RAID Controller

#7 2014-01-12 16:54:02

Re: [SOLVED] RAID Controller

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