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We have an active RAID 10 with four disks. Now we want to add one disk in RAID 0 to the adapter.

This is the current configuration:

# megacli -LDInfo -Lall -Aall


Adapter 0 -- Virtual Drive Information:
Virtual Drive: 0 (Target Id: 0)
Name                :
RAID Level          : Primary-1, Secondary-0, RAID Level Qualifier-0
Size                : 5.457 TB
Sector Size         : 512
Mirror Data         : 5.457 TB
State               : Optimal
Strip Size          : 64 KB
Number Of Drives per span:2
Span Depth          : 2
Default Cache Policy: WriteBack, ReadAhead, Direct, Write Cache OK if Bad BBU
Current Cache Policy: WriteBack, ReadAhead, Direct, Write Cache OK if Bad BBU
Default Access Policy: Read/Write
Current Access Policy: Read/Write
Disk Cache Policy   : Disk's Default
Encryption Type     : None
Default Power Savings Policy: Controller Defined
Current Power Savings Policy: None
Can spin up in 1 minute: Yes
LD has drives that support T10 power conditions: No
LD's IO profile supports MAX power savings with cached writes: No
Bad Blocks Exist: No
Is VD Cached: Yes
Cache Cade Type : Read Only



Exit Code: 0x00

Now we added another drive which we want to configure as RAID 0. (Enlarge RAID 10 was not possible, so we decided to add just another disk, where we can save backups and stuff).

The new disk is in slot 4:

Enclosure Device ID: 32
Slot Number: 4
Media Error Count: 0
Other Error Count: 0
Firmware state: Unconfigured(good), Spun Up
Inquiry Data:            24M9K179FTOSHIBA MG03ACA300                          FL1D

Is it save for the other RAID 10 array to create a new RAID 0 array with the following command (Enclosure 32, Slot 4):

megacli -CfgLdAdd -r0 [32:4] WB RA Direct CachedBadBBU -a0

We definitely do not want to hurt the existing RAID 10 array and do not want to loose any data in this.

Thank you very much!

seobility
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1 Answers1

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Yes, that's safe. The command you've created won't affect any other drives, though I wonder why you've elected to utilize a writeback cache regardless of BBU state for a backup drive (or ANY array, for that matter). Backups are typically sequential in the first place, and integrity is of a primary concern. Forcing a writeback cache will greatly increase the chances of corruption during power failure.

The only valid argument FOR this option in production is a battery backed server - but that's still dubious in practice. You should remove the option "CachedBadBBU" if you care about data integrity.

Spooler
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  • Thank you very much! Our hosting provider, which runs a wiki for common server tasks recommend to use this options when creating a raid array on Dell PERC H730: `WB RA Direct CachedBadBBU -a0` So we should use `WB RA Direct nocachedbadbbu -a0` instead? And of course there is a BBU. – seobility Oct 10 '16 at 14:02
  • You can just remove the option altogether, in most cases. It's the card firmware factory default to flush and disable the writeback cache when a BBU goes bad. You can check if that's the current firmware configuration default by looking through the output of `# megacli -AdpAllInfo -aALL`. If you need to, then yes you can override that value with `nocachedbadbbu`. However, it might be prudent to just change the default setting in that case. – Spooler Oct 10 '16 at 14:51