Re: Supermicro SAS controller
On Sun, 06 May 2012 17:44:54 +0000, Ramon Hofer wrote:
> On Sun, 06 May 2012 15:40:50 +0000, Camaleón wrote:
>> Okay. And how much space are you planning to handle? Do you prefer a
>> big pool to store data or you prefer using small chunks? And what about
>> the future? Have you tought about expanding the storage capabilities in
>> a near future? If yes, how it will be done?
>
> My initial plan was to use 16 slots as raid5 with four disks per array.
> Then I wanted to use four slots as mythtv storage groups so the disks
> won't be in an array.
> But now I'm quite fscinated with the 500 GB partitions raid6. It's very
> flexible. Maybe I'll have a harder time to set it up and won't be able
> to use hw raid which both you and Stan advice me to use...
It's always nice to have many options and true is that linux softare raid
is very pupular (the usual main problem for not using is when high
performance is needed and when doing a dual-boot with Windows) :-)
>>> You have drives of the same size in your raid.
>>
>> Yes, that's a limitation coming from the hardware raid controller.
>
> Isn't this limitation coming from the raid idea itself?
Well, no, software raid does not impose such limit because you can work
with partitions instead.
In hardware raid I can use, for example, a 120 GiB disk with 200 GiB disk
and make a RAID 1 level but the volume will be of just 120 GiB. (I lose
80 GiB. of space in addition to the 50% for the RAID 1 :-/).
> You can't use disks with different sizes in a linux raid neither? Only
> if you divide them into same sized partitions?
Yes, you can! In both, hardware raid and software raid. Linux raid even
allows to use different disks (SATA+PATA) while I don't think it's
recommended becasue of the bus speeds.
>> I never bothered about replacing the drive. I knew the drive was in a
>> good shape because otherwise the rebuilding operation couldn't have
>> been done.
>
> So you directly let the array rebuild to see if the disk is still ok?
Exactly, rebuilding starts automatically (that's a default setting, it is
configurable). And rebuiling always ends with no problem with the same
disk that went down. In my case this happens (→ the array going down)
because of the poor quality hard disks that were not tagged as
"enterprise" nor to be used for RAID layouts (they were "plain" Seagate
Barracuda). I did not build the system so I have to care about that for
the next time.
>>> My 6 TB raid takes more than a day :-/
>>
>> That's something to consider. A software raid will use your CPU cycles
>> and your RAM so you have to use a quite powerful computer if you want
>> to get smooth results. OTOH, a hardware raid controller does the RAID
>> I/O logical operations by its own so you completely rely on the card
>> capabilities. In both cases, the hard disk bus will be the "real"
>> bottleneck.
>
> I have an i3 in that machine and 4 GB RAM. I'll see if this is enough
> when I have to rebuild all the arrays :-)
Mmm... I'd consider adding more RAM (at least 8 GB) though I would prefer
16-32 GB) you have to feed your little "big monster" :-)
Greetings,
--
Camaleón
Reply to: