DL380 -- RAID and Number of DIsks

[scott_417]

For a DL 380, the online purchase confiuration indicates: "RIAD 5 drive set (require matching 3 hard drives)".

1) Is this # of matching disks is the minimum number?

2) If YES to 1), for the same RAID 5, can I include 4 disks?

3) If YES to 2), the maimux number of disks can afford to lose is ONE, i.e., in the event of crashing, the RAID 5 will survive the crashing by losing one, and no more than ONE disk. --Correct?

4) If each of the 4 disks in RAID 5 is 146 GB, the maimux capacity will be 3 x 146 GB (4 minus 1) --Correct?


Thanks.

[Igor Karasik]

1) Yes, 3 disk is minimum for RAID-5
2) Yes, RAID-5 may include 4 disks
3) Yes, no more than one disk
4) Yes, capacity will be 3*146

[Igor Karasik]

RAID ADG allows two drives to fail simultaneously without downtime or
data loss
See last question:
http://docs.hp.com/en/J6369-90025/apes01.html
"RAID ADG is an extension of RAID 5 that allows additional fault tolerance by using two different and independent parity schemes. Data is striped across a set of hard drives, just as with RAID 5, and the two sets of parity data are calculated and written across all the drives in the array.

RAID ADG provides an extremely high level of fault tolerance and can sustain two simultaneous drive failures without downtime or data loss. This fault tolerance level is the perfect solution when data is mission critical"

But DL380 by default have only 6i SmartArray controller which doesn't support RAID ADG. Only 640x controllers support RAID ADG (Of course you can buy 640x controlelr for your DL380 G4)

[Shameer.V.A · Accepted solution]

Hi scott,

Please find the following

1) Is this # of matching disks is the minimum number?

For Configuring RAID 5 minimum 3 disks are required

2) If YES to 1), for the same RAID 5, can I include 4 disks?

You can have n number of disks in RAID5 .Only limitation is the maximum free HDD slots in cage & Controller limitation ( per channel 15 disks)

3) If YES to 2), the maimux number of disks can afford to lose is ONE, i.e., in the event of crashing, the RAID 5 will survive the crashing by losing one, and no more than ONE disk. --Correct?

Yes. Your actual usable capacity willbe n-1 , if n is the # of disks used. But you shouldn't consider the whole raw disk capacity as the usable disk capacity (for eg: on a 36 Gb disk , the effective usable space is approx 34GB.) So if you configure 3*36Gb in RAID 5 you will get only 68GB effective not 72GB.

4) If each of the 4 disks in RAID 5 is 146 GB, the maimux capacity will be 3 x 146 GB (4 minus 1) --Correct?

Yes , But your effective usable capacity will be 384GB ( 3*136GB (effective usable space of a 146GB ).

You can configure a hot spare for your array. You have to spare one more hdd, which will automatically rebuild to your array , when any of the disk fails.

Hope this information help you

Regards,

Shameer

[Shameer.V.A]

Hi Scott,
Please find the following thread regarding the configuration of performance oriented queries.
Willbe useful..

Regards,

Shameer

[Linda Ruiz]

Can someone explain why then when I set my RAID-5 up with 5 drives + 1 hot spare I was able to actually lose 2 disks at once? For the first loss, it automatically switched to the hot spare. Then the for the second loss I believe it just had a red X on it. I believe I even hot-swapped out both at the same time and the array was rebuilt. Nothing was lost. This happened on a DL-380 Gen 3. It's been a while since that happened.

[David Claypool]

Your second failure must have happened after the hot spare was finished rebuilding. It was then a RAID 5 with no hot spare, so that second drive could fail. The original failure became a non-functional drive and the second one a failed drive, so you could swap both.

[scott_417]

Thank you all for the responses.

Then why 146 GB disk only has 136 GB effective usable space?

Thanks

Scott

[Shameer.V.A]

Hi Scott,
Sorry,
I forgot to attach the thread link in last reply. Pelase assign 0 point to that post.

Please find the following thread regarding the performance concern of RAID

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=986460

Regards,

Shameer