Re: [PLUG] RAID6 or RAID5+HS?

[Thomas Delrue <delrue.thomas@gmail.com>]

I hear great things about BTRFS with this RAID thing you mention :P

(I'll see myself out)

On 08/21/2016 04:07 PM, Rich Mingin (PLUG) wrote:
> If close together failures are a concern as you say at the end, RAID6 *is*
> RAID5+hot spare minus rebuild time. The extra I/O is largely offset by the
> extra disk sharing the load.
> 
> On Aug 21, 2016 4:01 PM, "JP Vossen" <jp@jpsdomain.org> wrote:
> 
>> Semi OT but my argument is that the OS going on the hardware is Debian...
>> :-)  Note, Debian Jessie requires "firmware-bnx2_0.43_all.deb" for the NICs
>> on the R710.  I haven't tested the R720 yet.
>>
>> I want to rebuild my VM server and the hardware I'll probably use is a
>> Dell PE R710 with 6x3T drives and a PERC H700 (2.02-0025) [1].  I can do
>> RAID6 or RAID5+hot-spare, and either way I should get about 11T out of it.
>> All are 7200RPM SATA disks.
>>
>> As I understand it, either RAID6 or RAID5+HS can handle losing 2 disks,
>> but:
>> * RAID6 has a write penalty for the extra parity block
>> * Hot-spare has a gap while the array rebuilds onto the hot-spare
>>
>> The use-case is my main VMware server (Debian Jessie + LXDE + VMware
>> Workstation 10.x [2].  The critical VM is my main "services" server (DNS,
>> DHCP, file&print, etc., also Jessie) and the next important one will be my
>> MythTV backend (Mythbuntu 14.04), once I virtualize it [3]. Everything else
>> is just test VMs and whatever.  I do not backup the contents of the MythTV
>> server because it's too big, but everything else is backed up in a few
>> different ways (BackupPC, BoxBackup, rsync).  I've got 1.5T in VMs and 3T
>> in MythTV, so 11T is lots of room.
>>
>> I don't do a lost of disk-intensive things.  Probably MythTV recording 2
>> shows at once while playing a third is the worst, but I really don't have a
>> good sense of the relative load and capacities of all the parts involved.
>>
>> This will be most of my eggs in one basket, so I'd really like tolerance
>> for 2 disks to fail close together.  So...RAID6 or RAID5+HS?  Any other
>> random thoughts?
>>
>> Thanks,
>> JP
>> _____________________________________________________
>> Footnotes:
>>
>> [1] I might also be able to use an R720 with 8x4T drives, but that has 1
>> bad drive already and I may end up using that for a $WORK thing.  It was
>> drawing 150-180 watts during a RAID init, but I'd like to re-test with an
>> OS with CPU scaling installed and running.
>>
>>
>> [2] I know that in theory I could use ESXi, but:
>> 1) I have 100+ VMs with many snapshots, and I don't know of any way to
>> move those VMs from Workstation into ESXi without:
>>         1.1) doing it manually and
>>         1.2) losing snapshots (show stopper)
>> 2) The last time I tried using ESXi (5.x IIRC) I found it impossible to do
>> anything useful in it
>> 3) I do not have, nor will I have, any Windows involved in any VM control
>> or management, or anything important
>>
>> Those last two may have changed since newer ESXi has the web GUI and not
>> the fat Windows client.  But the show-stopping snapshot issue remains.
>>
>>
>> [3] MythTV is currently on a PE2950 with 6x1T drives in RAID5, but the
>> unit is drawing about 300 watts.  My current R710 with 6x1T RAID5 is
>> drawing about 140 watts, so I really wish I'd bothered to put the
>> kill-a-watt on them sooner.  All have dual power supplies so the test is
>> easy (and yes, I unplugged the non-kill-a-watt supply for the test).

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