Server won't boot after 2 drives in raid 10 failed...

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Hi all,

A mate of mine just phoned to say he has a server that won't boot.

He has 4 drives in raid 10, 2 have failed and the server will not boot.

I always thought you could lose 2 drives and still be ok?

Cheers,

G
 
if i remember rightly on a raid10 if one of the mirrors loses all of its drives the array is broken? as its 2 out of 4 disks it may be that one of the mirrors has been taken out.
 
RAID 10 is just a RAID 1 and RAID 0, layered together.

So if he has had two drive failures and cannot rebuild the array, then it sort of suggests that the drives that have died were both paired with RAID 1. So he has lost one half of his RAID 0 stripes.

He is about to have a very bad day, I think.
 
NathanE said:
RAID 10 is just a RAID 1 and RAID 0, layered together.

So if he has had two drive failures and cannot rebuild the array, then it sort of suggests that the drives that have died were both paired with RAID 1. So he has lost one half of his RAID 0 stripes.

He is about to have a very bad day, I think.
Click to expand...

Yup agreed, how unlucky is that! I hope he had some tape backup or what not....

Stelly
 
Sorted it now.

Ended up going down there and removing one of the HDD as it was cold to the touch.

All working now new HDD ordered.
 
I think a lot of you need to go back and work out what is RAID 10. Please explain how raid 10 can't sustain two disk failures: as I can't work out you're logic at all (this is aimed at every bar the OP).

RAID 10 with 4 disks:

Disk 0 - Data "RI"
Disk 1 - Data "RI"
Disk 2 - Data "AD"
Disk 3 - Data "AD"

Disk 0 is mirrored with Disk 1. (RAID 1)
Disk 2 is mirrored with Disk 2. (RAID 1)

But the data is written to the drives stripped. So one mirror contains half the data, above DATA = RAID.

So, Any two failures of disks regardless will work.
 
ecksmen said:
I think a lot of you need to go back and work out what is RAID 10. Please explain how raid 10 can't sustain two disk failures: as I can't work out you're logic at all (this is aimed at every bar the OP).

RAID 10 with 4 disks:

Disk 0 - Data "RI"
Disk 1 - Data "RI"
Disk 2 - Data "AD"
Disk 3 - Data "AD"

Disk 0 is mirrored with Disk 1. (RAID 1)
Disk 2 is mirrored with Disk 2. (RAID 1)

But the data is written to the drives stripped. So one mirror contains half the data, above DATA = RAID.

So, Any two failures of disks regardless will work.
Click to expand...

RAID 10 is a stripe of mirrors.

With 4 drives (for simplicity) you can lose one drive from each mirror and it keeps running because the stripe is intact. If you lose two drives from the same mirror you’ve lost one half of the stripe and it fails.

(I think)

From your example if disks 0 & 1 both failed you'd only have "AD" the array would break. Likewise if disks 2 & 3 both failed you'd only have "RI".
 
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ecksmen said:
I think a lot of you need to go back and work out what is RAID 10. Please explain how raid 10 can't sustain two disk failures: as I can't work out you're logic at all (this is aimed at every bar the OP).

RAID 10 with 4 disks:

Disk 0 - Data "RI"
Disk 1 - Data "RI"
Disk 2 - Data "AD"
Disk 3 - Data "AD"

Disk 0 is mirrored with Disk 1. (RAID 1)
Disk 2 is mirrored with Disk 2. (RAID 1)

But the data is written to the drives stripped. So one mirror contains half the data, above DATA = RAID.

So, Any two failures of disks regardless will work.
Click to expand...

No, everything you just posted there makes sense except the conclusion you draw from it. If Disk 0 and Disk 1 die, you lose everything. If Disk 2 and Disk 3 die, you lose everything. It's that simple. It's down to luck really. If you have two disks fail in a RAID 10 array then you better hope the two affected disks aren't mirroring the same stripe data.

450px-RAID_10_6Drives.svg.png


http://aput.net/~jheiss/raid10/
http://en.wikipedia.org/wiki/Nested_RAID_levels#Redundancy_and_data-loss_recovery_capability
 
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Ah... so because it's striped each mirror only contains half of the data being saved to the disk. So if one mirror goes completely so does half the data hence complete failure.

I think I get it now.

Would be mega harsh to have 2 disks fail in the same mirror then!

Thanks,


G
 
Its fairly likely (and unlucky) to lose two in a short time as the most stressful point in a disks life can be rebuilding another disk that has failed in a raid array.

Hence why a lot of decent SAN's and NAS's have DP.
 
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masterk said:
Its fairly likely (and unlucky) to lose two in a short time as the most stressful point in a disks life can be rebuilding another disk that has failed in a raid array.

Hence why a lot of decent SAN's and NAS's have DP.
Click to expand...

DP?

I'm pretty sure you don't mean the term I'm thinking of lol
 
Agreed on the domino effect.

Swapped a drive out in a server at work. Array finished rebuilding and within hours another had gone down.

Managed to convince them to buy a new server so not all bad :)
 
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