[ale] raid suggestions

[Derek Atkins]

Pat Regan <thehead at patshead.com> writes:

> On Wed, 15 Feb 2012 09:44:22 -0500
> "mike at trausch.us" <mike at trausch.us> wrote:
>
>> I have a RAID 6 array that is somewhat slow, but I know _precisely_
>> why it is slow and it has nothing to do with the kernel; the
>> bottleneck in this case is the SATA port multiplier, and without
>> spending a little more money there is nothing that I can do about it.
>
> Since we're speaking about corner cases and odd hardware problems...
>
> I've been using the same motherboard in my home file server (aka, my
> arcade cabinet these days) for 4-5 years.  It has 6 SATA ports and
> started life with a 4 drive RAID 5.  Performance was still good when I
> added a 5th drive.  Adding a 6th drive didn't go so well...
>
> The initial resync took forever and read speeds plummeted to about the
> speed of a single drive.  Usually read speeds go up as you increase
> drive count and fresh write speed stays pretty constant.
>
> I didn't really care about the performance at the time, it usually only
> had to keep up with my 100 megabit switch or my wifi.  The problem did
> straighten itself out at some point, though, during a kernel upgrade.
> I'm assuming the problem was some sort of driver inefficiency.

I've got a RAID-10 setup and the only time I see performance issues is
on large-scale I/O.  For example if I am copying a large multi-GB file
then it can bring the system to a screetching halt.  Alternatively, I
will also see it if I am doing a VM Suspend operation, or a VM restore
operation, where it has to read GBs of data at once.  I haven't spent
the time to figure out what's going on.

> Pat

-derek

-- 
       Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
       Member, MIT Student Information Processing Board  (SIPB)
       URL: http://web.mit.edu/warlord/    PP-ASEL-IA     N1NWH
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