[CentOS] new "large" fileserver config questions

[Rafa Griman]

Hi :)

On Tue, Oct 2, 2012 at 8:47 PM, Keith Keller
<kkeller at wombat.san-francisco.ca.us> wrote:
> On 2012-10-02, John R Pierce <pierce at hogranch.com> wrote:
>>
>> a server makes very little use of its system disks after its booted,
>> everything it needs ends up in cache pretty quickly.  and you typically
>> don't reboot a server very often.   why waste SSD for that?
>
> I think the impetus (which I wasn't totally on top of) was to maximize
> the number of drive bays in the controller node.  So the bays are 2.5"
> instead of 3.5", and finding 2.5" ''enterprise'' SATA drives is fairly
> nontrivial from what I can tell.  I don't actually need 8 2.5" drive
> bays, so that was an oversight on my part.
>
> After reading the SSD/RAID docs that John Doe posted, I am a little
> concerned, but I think my plan will be to use these disks as I
> originally planned, and if they fail too quickly, find some 2.5"
> magnetic drives and RAID1 them instead.  I may also end up putting /tmp,
> /var, and swap on the disk array instead of on the SSD array, and treat
> the SSD array as just the write-seldom parts of the OS (e.g., /boot,
> /usr, /usr/local).  If I do that I should be able to alleviate any
> issues with excessive writing of the SSDs.


If it works with you ... I mean, there's no perfect partition scheme
(IMHO), depends greatly on what you do, your budget, workflow, file
size, ... So if you're happy with this, go ahead. Just some advice:
test a couple of different options first just in case ;)


> I am not sure what drives I have, but I have seen claims of "enterprise"
> SSDs which are designed to be up 24/7 and be able to tolerate more
> writes before fatiguing.  Has anyone had experience with these drives?
>
>> re: alignment, use the whole disks, without partitioning.   then there's
>> no alignment issues.   use a raid block size of like 32k. if you need
>> multiple file systems, put the whole mess into a single LVM vg, and
>> create your logical volumes in lvm.
>
> So, something like mkfs.xfs will be able to determine the proper stride
> and stripe settings from whatever the 3ware controller presents?


Yup, even though you've got the sw and su options in case you want to
play around ... With XFS, you shouldn't have to use su and sw ... in
fact you shouldn't have to use many options since it tries to
autodetect and use the best options. Check the XFS FAQ.


>  (The
> controller of course uses whole disks, not partitions.)  From reading
> other sites and lists I had the (perhaps mistaken) impression that this
> was a delicate operation, and not getting it exactly correct would cause
> performance issues, possibly set fire to the entire data center, and
> even cause the next big bang.


Nope, just mass extinction of the Human Race. Nothing to worry about.

HTH

   Rafa