Help! One of my RAID 5 HDDs died on me ...


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Adam Goi

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#1
Hi ...

One of my 2 HDDs on RAID 5 died on me so when I tried to boot up, it's simply no go ... so I installed a new HDD w/o RAID.

My question is will I be able to retrieve the data from the remaining healthy ex-RAID 5 based HDD? If yes, how do I go about doing it?

TIA!
 

satay16

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Jan 14, 2006
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#2
hmmm........2 disks running on raid 5? sounds abit impossible.
 

Dennis

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Jan 24, 2002
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#3
I can feel how you feel. :(
My NAS also died on me recently but hopefully the data is still intact.
I have 4 HDD running Raid 5 but my NAS motherboard died.
BTW if you are running Raid5 you should be able to rebuild your data but 2 HDD you probably can't run raid 5.:dunno:
 

#6
I can feel how you feel. :(
My NAS also died on me recently but hopefully the data is still intact.
I have 4 HDD running Raid 5 but my NAS motherboard died.
BTW if you are running Raid5 you should be able to rebuild your data but 2 HDD you probably can't run raid 5.:dunno:
It shouldn't be a problem, just replace with the same mobo, the RAID should still be fine, you have 1 spare right? Then pretty safe.

RAID 5 is min 3 HDD. 2 HDD cannot do RAID 5 :bsmilie:
 

matthew

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Apr 19, 2002
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#7
hmmm........2 disks running on raid 5? sounds abit impossible.
It is. (Although I have just found a reference that says 2 disk RAID 5 IS possible, but they may mean a 3 disk RAID 5 with one failed drive is still usable.)

It was either 'RAID 0' striping which has no redundancy at all, or RAID 1 mirroring. If it was RAID 1 the system should still boot.

If it was RAID 0, all data is now lost, as only every 2nd block still exists on the remaining good drive.

Adam - if you were getting the storage of both drives joined together on your system it was not redundant and your data is lost, as it was either a 'JBOD' or RAID 0 which has no redundancy.

With a RAID 1 setup, you have redundancy against a drive failure, but can only use the space of one drive, as the 2nd one is the 'backup'.

RAID 5 is the generally accepted compromise between redundancy and space, but you can't implement it with less than 3 (identical) disk drives.

The only way to get the data back if it was RAID 1 is to get the failed drive repaired with data intact. Expensive :)
 

V

vince123123

Guest
#8
I have always wondered, for RAID 5, if one disk fails, MUST you get the same IDENTICAL brand/model/size HDD to replace the failed one? Some say yes, some say no. What's the answer?

If the answer is yes, and by the time it fails, you can no longer find the same brand/model/size (highly forseeable since it may take a couple of years for failure to occur), is it then possible to copy out the EVERYTHING that is on the remaning drives, to a new HDD set? I heard that thsi may be possible, but that its going to be slow as the system has to extrapolate in order to copy everything (much like rebuilding a RAID array).

Hope some guru in this field can advise.
 

matthew

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Apr 19, 2002
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#9
I have always wondered, for RAID 5, if one disk fails, MUST you get the same IDENTICAL brand/model/size HDD to replace the failed one? Some say yes, some say no. What's the answer?

Hope some guru in this field can advise.
In general (RAID 5 controller permitting) the replacement drive HAS to have the same or larger block count than the old one. Smaller will simply not work at all. If the replacement has extra blocks (i.e. it is a bigger drive), it will work, but the extra space will be unusable and wasted.

You may run into some controllers that will allow the extra space to be used as a 'normal' non RAID partition, and conversely some controllers may enforce near identical drives in the set for performance reasons. (eg the controller wants near identical transfer and seek rates across all drives in the set).

I have run into a problem where the replacement drive supplied to me on paper had the same capacity as the dead original but for some reason the RAID controller thought this new drive was 4 blocks smaller than the original thus wouldn't accept it.
As an temporary fix to get this server running at full speed again, a drive of twice the capacity was fitted to the RAID set (and 70gb of space 'wasted') while various dealers argued over what 70Gb capacity really meant.
 

V

vince123123

Guest
#11
So what you'er saying is that I don't have to use back the same drive/model/brand/size that I used for the rest of the array? ie, I build the array with 2007 model HDD, in 2010 it fails. I can just get a larger 2010 drive and put it in? I dont mind wasted space, as long as the data is recoverable.

Also, it may not be practical to keep a 2007 model HDD as spare - first is waste of resources, 2nd when it comes to 2010, you never know if your 2007 spare is still working. Unless maybe you plug in the 2007 model all the time, then scarly your 2007 spare fail before the array....lol

In general (RAID 5 controller permitting) the replacement drive HAS to have the same or larger block count than the old one. Smaller will simply not work at all. If the replacement has extra blocks (i.e. it is a bigger drive), it will work, but the extra space will be unusable and wasted.

You may run into some controllers that will allow the extra space to be used as a 'normal' non RAID partition, and conversely some controllers may enforce near identical drives in the set for performance reasons. (eg the controller wants near identical transfer and seek rates across all drives in the set).

I have run into a problem where the replacement drive supplied to me on paper had the same capacity as the dead original but for some reason the RAID controller thought this new drive was 4 blocks smaller than the original thus wouldn't accept it.
As an temporary fix to get this server running at full speed again, a drive of twice the capacity was fitted to the RAID set (and 70gb of space 'wasted') while various dealers argued over what 70Gb capacity really meant.
 

KorgT3

New Member
Sep 30, 2006
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#12
Yes, you need not use exactly the same old model. Use a newer model with same or more disk space will work.
Secondly make sure the speed (rpm) of the replacing HDD is same or higher then the existing config.
Good Luck!
 

Sep 19, 2003
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#13
Hi ...

One of my 2 HDDs on RAID 5 died on me so when I tried to boot up, it's simply no go ... so I installed a new HDD w/o RAID.

My question is will I be able to retrieve the data from the remaining healthy ex-RAID 5 based HDD? If yes, how do I go about doing it?

TIA!

Raid 5 on 2 disk kinda unlikely..

But if you want to recover a marginally working hdd, a typically fast and dirty method i use is to use norton ghost to clone to a similar harddisk. As ghost is a low level copy, sometimes can recover 99% of the data in the old hdd.

ideally have raid 10 or something.. with hot backup or offsite mirrorring :D
 

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