what happens when a raid 1 fails?

Sorak · 30th July 2012, 9:59 PM

its just occured to me that ive never experienced a raid 1 failure.
if one drive dies is the other one still accessable or am i required to connect a second drive back in? also what happens if i just remove one? does it automatically unraid?

i got two different raid 1's set up, one through windows and one through the bios.

Renza · 30th July 2012, 10:09 PM

windows software raid 5

for my hardware raids, the array will work when one drive has dropped out, but will be in degraded state, and performance drops a little. insert a new drive and it will rebuild. if two drives fail, your data is toast, time to bring out the backups.

there's no real way to 'unraid' the drives short of backing up the data, destroying the array, and copying the data back onto the individual drives

sotech · 30th July 2012, 10:12 PM

Quote:

Originally Posted by Sorak

its just occured to me that ive never experienced a raid 5 failure.
if one drive dies is the other one still accessable or am i required to connect a second drive back in? also what happens if i just remove one? does it automatically unraid?

i got two different raid 5's set up, one through windows and one through the bios.

"Other one"? raid5 is a minimum of 3 drives - do you mean raid1 (mirror)?

Sorak · 31st July 2012, 6:11 PM

Quote:

Originally Posted by sotech

"Other one"? raid5 is a minimum of 3 drives - do you mean raid1 (mirror)?

*face palm* should have realised that.

yeah raid 1. sorry

phrosty-boi · 31st July 2012, 8:55 PM

raid works differently to normal drives, the OS typically sees the raid as 1 disk or volume rather than a group of disks (as far as filesystems are concerned anyway)

the OS may mark it as being degraded but it will still operate as normal

if you remove the 2nd disk to replace it you shouldnt notice anything different, it will just stay marked as degraded until it rebuilds

rowan194 · 31st July 2012, 9:02 PM

All RAID levels (excepting RAID0) will continue to function if only one drive fails. RAID5 and RAID6 can handle multiple failures without causing the array to die.

So your RAID1 array should be just fine if a drive fails, but you do need to do an immediate backup (for safety) and replace the drive ASAP.

RAID1 is a simple mirror, so with most implementations it is possible to connect one of its members to a non-RAID port and still be able to access the data. No other RAID levels can do this.

Stanza · 31st July 2012, 9:22 PM

Quote:

Originally Posted by rowan194

All RAID levels (excepting RAID0) will continue to function if only one drive fails. RAID5 and RAID6 can handle multiple failures without causing the array to die.

RAID 6 can handle multiple drives (2) failing, RAID 5 just one.

.

rowan194 · 31st July 2012, 9:53 PM

Quote:

Originally Posted by Stanza

RAID 6 can handle multiple drives (2) failing, RAID 5 just one.

.

Whoops... I meant to say something like - RAID5/6 need multiple drives to fail before the array is toast, but I got that all muddled up.

To reiterate...

RAID1, RAID5, ZFS RAIDZ1 will tolerate one drive failure without losing data.
RAID6, ZFS RAIDZ2 will tolerate two drive failures without losing data.
ZFS RAIDZ3 will tolerate three drive failures without losing data.

Jim G · 1st August 2012, 11:59 AM

Quote:

Originally Posted by rowan194

Whoops... I meant to say something like - RAID5/6 need multiple drives to fail before the array is toast, but I got that all muddled up.

To reiterate...

RAID1, RAID5, ZFS RAIDZ1 will tolerate one drive failure without losing data.
RAID6, ZFS RAIDZ2 will tolerate two drive failures without losing data.
ZFS RAIDZ3 will tolerate three drive failures without losing data.

One extra point - Raid1 will tolerate all but one drive failing - it is not uncommon to see 3-way mirrors for performance and redundancy which could survive a 2-disk failure.

rowan194 · 1st August 2012, 3:09 PM

Quote:

Originally Posted by Jim G

One extra point - Raid1 will tolerate all but one drive failing - it is not uncommon to see 3-way mirrors for performance and redundancy which could survive a 2-disk failure.

Good point, although bear in mind that simple "onboard" RAID will generally limit you to the classic 2 drives only.

I ran a 4 disk RAID1 array for performance for a while.

Davo1111 · 1st August 2012, 4:01 PM

as far as i've heard, the raid card beeps, lights up the effected port. replace the drive, and it starts mirroring from the non failed drive.

could be wrong though

Iron_Horse · 6th August 2012, 12:14 AM

In my experience the system may slow down.
Remove the affected drive and the RAID controller will now tell you that it is degraded.

Put in a new disk and it should automatically rebuild. Performance will take a hit but once it is up and going you should be good.

rowan194 · 6th August 2012, 2:10 AM

A degraded RAID1 array generally won't slow things down. You will probably notice performance suffer during a rebuild, though.

A degraded RAID5/RAID6 array is more apparent as it needs to read data from all the remaining drives in order to rebuild parity.

Iron_Horse · 7th August 2012, 11:16 AM

Quote:

Originally Posted by rowan194

A degraded RAID1 array generally won't slow things down. You will probably notice performance suffer during a rebuild, though.

A degraded RAID5/RAID6 array is more apparent as it needs to read data from all the remaining drives in order to rebuild parity.

In this case the SCSI disk I was using was also causing a blue screen which was odd. Did a swap and it was fine.

30th July 2012, 9:59 PM	#1
Sorak Member Join Date: Dec 2008 Location: Victoria 3161 Posts: 917	what happens when a raid 1 fails? its just occured to me that ive never experienced a raid 1 failure. if one drive dies is the other one still accessable or am i required to connect a second drive back in? also what happens if i just remove one? does it automatically unraid? i got two different raid 1's set up, one through windows and one through the bios. __________________ i7 920 @ Stock \| X58-UD5 \| XMS3 6GB @ 1066 \| GA-5870 \| Xonar D2X \| 450gb SanDisk Extreme \| 2x Samsung 2443BW \| Win 7 Last edited by Sorak; 31st July 2012 at 6:12 PM. Reason: "raid 5" changed to "raid 1"

30th July 2012, 10:09 PM	#2
Renza Member Join Date: Dec 2004 Location: Adelaide, 5051 Posts: 2,974	windows software raid 5 for my hardware raids, the array will work when one drive has dropped out, but will be in degraded state, and performance drops a little. insert a new drive and it will rebuild. if two drives fail, your data is toast, time to bring out the backups. there's no real way to 'unraid' the drives short of backing up the data, destroying the array, and copying the data back onto the individual drives __________________ i7 3770K @ 4.5ghz \| AsRock Z77 Professional \| 16gb Corsair Vengence 1600mhz \| Gigabyte GTX580 \| Seasonic X750 \| Silverstone TJ07 \| Crucial M4 256GB \| 2x Dell 2407WFP Canon 5D Mark II \| Canon EF 24-70 f/2.8L \| Canon EF 17-40 f/4L \| Canon EF 70-200 f/2.8L IS \| Canon EF 50mm f/1.8 \| Canon EX-580II \| Manfrotto 190 Pro B Traded over $22,000 on OCAU! - PM for recent traders

31st July 2012, 8:55 PM	#5
phrosty-boi Member Join Date: Jun 2003 Location: Melbourne - Gatso capital Posts: 894	raid works differently to normal drives, the OS typically sees the raid as 1 disk or volume rather than a group of disks (as far as filesystems are concerned anyway) the OS may mark it as being degraded but it will still operate as normal if you remove the 2nd disk to replace it you shouldnt notice anything different, it will just stay marked as degraded until it rebuilds __________________ Good trades - sab988, cgd, garnet, RayEarth

6th August 2012, 12:14 AM	#12
Iron_Horse Member Join Date: Oct 2005 Location: Onboard the Borg ship... Posts: 686	In my experience the system may slow down. Remove the affected drive and the RAID controller will now tell you that it is degraded. Put in a new disk and it should automatically rebuild. Performance will take a hit but once it is up and going you should be good. __________________ Psalm 51:15: O Lord, open my lips, and my mouth shall show forth Your praise. Psalm 116:12-13: How can I repay the LORD for all his goodness to me? I will lift up the cup of salvation and call on the name of the LORD.

31st July 2012, 9:02 PM	#6
rowan194 Member Join Date: Jan 2009 Posts: 1,872	All RAID levels (excepting RAID0) will continue to function if only one drive fails. RAID5 and RAID6 can handle multiple failures without causing the array to die. So your RAID1 array should be just fine if a drive fails, but you do need to do an immediate backup (for safety) and replace the drive ASAP. RAID1 is a simple mirror, so with most implementations it is possible to connect one of its members to a non-RAID port and still be able to access the data. No other RAID levels can do this.

1st August 2012, 4:01 PM	#11
Davo1111 Member Join Date: Mar 2009 Location: Syd Posts: 2,598	as far as i've heard, the raid card beeps, lights up the effected port. replace the drive, and it starts mirroring from the non failed drive. could be wrong though

6th August 2012, 2:10 AM	#13
rowan194 Member Join Date: Jan 2009 Posts: 1,872	A degraded RAID1 array generally won't slow things down. You will probably notice performance suffer during a rebuild, though. A degraded RAID5/RAID6 array is more apparent as it needs to read data from all the remaining drives in order to rebuild parity.