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I have a HP Proliant DL 380 G7 Server with a RAID 5 that has 2 failed disks.
My Question is, can i reduce the array to 3 hard disks that are remaining to work with them alone? Can I do this without loosing any data in the hard disks?

ewwhite
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Carey
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3 Answers3

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No. RAID5 can only tolerate the loss of one disk (and occasionally, not even that many).

Your array is failed, and the data on it is gone.

So, the important thing here is that you learn from this mistake.

  1. RAID IS NOT A BACKUP! So take backups of all the data you care about.

  2. If your monitoring system had alerted you when the first drive failed, you'd probably have been able to replace the drive. A properly configured monitoring/alerting system is invaluable.

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HopelessN00b
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  • Thanks for your advice, i will learn from this. So its not possible even to recover the data that was there? – Carey Jan 08 '13 at 15:54
  • Thanks for your advice, i will learn from this. So its not possible even to recover the data that was there? – Carey Jan 08 '13 at 16:03
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    @user152508 Not without shipping the drives to a data recovery firm (that would charge thousands of dollars to try). If the data's *that* valuable, it might be worth letting them try to pull data off the platters of the failed drives for that price, but otherwise, one quarter of the data on the array is just gone, and the other 3 quarters is essentially scrambled by the absences of the failed disks. – HopelessN00b Jan 08 '13 at 16:07
  • hopelessn00b, yer i know i don't think they would use that much money for recovery. so the scrambled data can also not be recovered? – Carey Jan 08 '13 at 16:11
  • @user152508 It's a little more complicated than that - but basically RAID5 writes the disk data in chunks. So you'll have chunks missing out of the existing data on the remaining disks, and those chunks won't line up with anything that would make sense from the perspective of the file system. Half a file here, a little bit of a file there, etc. So... you're not going to recover much meaningful. [See the image here for an idea of what the data "looks like," and how it's "scrambled."](http://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_5) – HopelessN00b Jan 08 '13 at 16:23
  • hopelessn00b, thank you so much, i understand. its a bad day. Would i be able to recover the raid if i only lost one hard disk? – Carey Jan 08 '13 at 16:27
  • if you only lost one disk, the array would still be functional (albeit slower). – Rex Jan 08 '13 at 16:28
  • @Rex, how? in my comp after boot it tell me invalid system disk then it reboots – Carey Jan 08 '13 at 16:30
  • your question to hopeless was if you would be able to recover the array if you had lost one hard disk. The answer to that is yes, a RAID5 array should continue to function after losing only a single drive. In your case, you lost 2 drives and therefore, you lost your array. – Rex Jan 08 '13 at 19:39
  • @Rex its only that i am not sure if i have lost two hard disks, i think i have lost only one. when i boot the computer only one hard disks lights up funny. how can i return the raid? i now have a new hard disk of same capacity – Carey Jan 09 '13 at 10:36
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That depends entirely on the type of array you have.

For an array of N disks, each type of RAID offers different levels of protection against the loss of one or more of those disks.

The currently in-use types of RAID are as follows:

RAID-1 (mirroring): N > 1; duplicates all data to all mirror disks. You can lose up to N-1 disks.

RAID-10 (striped mirroring): N > 3 and N is even; mirrors pairs of disks and stripes all mirrors into a larger array. You can lose one disk from each pair, up to N/2, but not both disks from a pair.

RAID-5 (striping with parity): N > 2; parity (error recovery) data is written for every N-1 stripes; you can lose up to 1 disk.

RAID-6 (striping with double parity): N > 3; parity data is written to two stripes for every N-2; you can lose up to 2 disks.

There are other, more obscure versions in use, such as RAID-1e and RAID-5e that don't follow such straight 1-to-1 assignments of stripes vs. drives, but it's unlikely you have one of those unless you already know the answer to your question.

adaptr
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  • That's not quite accurate, or complete. There are variants of mirror RAID that can use odd numbers of disks, for example (look up RAID 1e). – HopelessN00b Jan 08 '13 at 15:48
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    Consider the odds the asker of this question knows the difference. – adaptr Jan 08 '13 at 15:49
  • Right, but for the sake of future Googlers and such... – HopelessN00b Jan 08 '13 at 15:50
  • Could you make this discussion a bit simple for me to understand? Yes i understand my data is gone, but for future i would like to know – Carey Jan 08 '13 at 15:53
  • Agreed, but I answered before he divulged the fact that it was R5. I can't hardly edit my response without making it completely obsolete :( – adaptr Jan 08 '13 at 15:53
  • Thanks for your advice, i will learn from this. So its not possible even to recover the data that was there? – Carey Jan 08 '13 at 16:06
  • adaptr, you have made me understand it well, thank you. by the way, am totally green, i dont know the answer. How would i do the recovery if i lost only one hard disk? coz one of them seems like it can work(it blinks a green light) – Carey Jan 08 '13 at 16:20
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If all else fails... try powering the system off, removing power for a few minutes and powering back on again.

These drives failed, but probably not at the same time. How long did you go before noticing or taking action? How do you know the drives have failed? Red LED light? Insight Manager report?

There are some odd firmware/controller combinations where disks report false failures. Your firmware probably isn't up-to-date, but if the server is still running, it's worth looking at updates.

ewwhite
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  • ewwhite, i now they have failed because the server just keeps saying non system disk and the hard disks are not showing any light at all – Carey Jan 08 '13 at 17:07
  • Power off and back on... and pay VERY close attention to the POST messages during boot. When prompted with "Press any key to view Option ROM messages", press any key. THe RAID controller will tell you what its status is at that point. [See this answer for screenshots.](http://serverfault.com/questions/391894/cant-enter-ilo3-at-bootup-hp-proliant-dl360-g7/392099#392099) – ewwhite Jan 08 '13 at 17:13
  • ewwhite, i did the powering of then on. it did not ask me to press any key, i also noticed the screenshort is different from the one i am seeing, i have two servers the one with the issue is g6 not g7 sorry. after displaying the raid error it went to the non system disk error – Carey Jan 08 '13 at 18:17
  • ewwhite, could you please continue assisting me? i am not sure i have lost 2 hard disks, i think i have lost only one – Carey Jan 09 '13 at 10:37
  • Can you provide a screenshot of the RAID controller error? – ewwhite Jan 09 '13 at 11:14