Re: Supermicro SAS controller
On Fri, 04 May 2012 15:38:10 +0000, Camaleón wrote:
> On Fri, 04 May 2012 10:48:36 +0000, Ramon Hofer wrote:
>
>> On Thu, 03 May 2012 20:27:02 +0000, Camaleón wrote:
>
>>> There's some useful information in one of the links I sent before:
>>>
>>> http://wiki.debian.org/LinuxRaidForAdmins
>>
>> Maybe I miss something but the page doesn't say anything about cli
>> tools of the megaraid cards :-?
>
> Yes... no info is also info after all. Not the one you'd like to read
> but that's how it is :-). Anyway, the page can be simply outdated or
> lacking from that specific information.
>
> Also, the expanded information on the "megaraid_sas" driver points to
> the page you sent before:
>
> http://hwraid.le-vert.net/wiki/DebianPackages
>
> Where you can find a set of tools for your driver ("megaclisas-status"
> and "megacli") as well as more information about the LSI controllers and
> the driver status:
>
> http://hwraid.le-vert.net/wiki/LSIMegaRAIDSAS
>
> Ufff, I was not aware of this:
>
> ***
> There is currently no known opensource tool for theses cards. ***
>
> How, how bad... in contrast, 3ware seems to fully support open source,
> or at least that's what it can be read here:
>
> http://hwraid.le-vert.net/wiki/3Ware
>
> ***
> 3Ware supports Linux and provide an opensource kernel driver which has
> been part of Linux for ages
> ***
>
> This is something to reconsider.
Yes, this is really not what I wanted to read :-o
So I think I'll just go for the LSI card and use mdadm. The 3Ware card I
found at my dealer was twice the price of the LSI...
<snipped>
>>> Just an additional note. By reading the chosen card specs it seems it
>>> does not support a RAID 6 level (which is better than RAID 5 because
>>> it allows the failure 2 disks) so that can be a handycap.
>>
>> This should be no problem. I plan to use four slots without raid for
>> mythtv.
>> I already have a 4x 1.5 TB disks raid 5 and another 4x 2 TB disks raid
>> 5. When I want to add more disks I can e.g. go for 3 TB disks and set 4
>> of them up as another raid5.
>> Like this I can use disks with different sizes.
>
> Just a note of caution here.
>
> RAID 5 with big hard disks can be a real pain and a real problem. If one
> of the arrays go down, the rebuilding operation can take up to "days"
> (depending on the controller's capacity) and if while the RAID is
> rebuilding a second disk of the array is also down for whatever reason
> (it can be a false possitive) you can't recover your data, at least not
> that easily. That's why most people is switching from raid 5 to raid 6,
> it adds an extra of security with no remarkable drawbacks.
That's true.
On the other hand it isn't possible to have different disk sizes in a
raid 6 neither.
So my plan seems still reasonable to me to have several 4 disks raid 5
arrays. Like that I'm flexible to add bigger disks in future as they
become cheaper and still can keep my old 1.5 TB disks.
And if I would go for raid 6 with the 4 disk array I would loose a third
of the capacity.
>> I'm thinking of combining the arrays then to a lvm... But I don't know
>> if this is a good idea as it adds more complexity :-?
>
> Yes, it will be a good idea (it will allow you to manage your volumes in
> a more flexible manner) and yes, it will add an extra layer of
> complexity (RAID+LVM) :-)
Ok, hope it won't be too complicated :-)
Best regards
Ramon
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