Re: potentially lost largeish raid5 array..

[Stan Hoeppner <stan@hardwarefreak.com>]

On 9/23/2011 11:22 AM, Thomas Fjellstrom wrote:

> I'd love to switch, but I didn't really have the money for the card then, and
> now I have less money. I suppose if I ebayed this card first, and then bought a
> new one that would work out, but yeah, It will have to wait a bit (things are
> VERY tight right now).

Which is why you purchased the cheapest SAS card on the market at that 
time. :)

> So this Intel card, looks like a good option, but how much faster is it? I get
> 500MB/s read off this SASLP. Probably a bit more now that there's 7 drives in
> the array. Off of XFS, it gets at least 200MB/s read (the discrepancy between
> raw and over xfs really bugs me, something there can't be right can it?).

When properly configured XFS will achieve near spindle throughput. 
Recent versions of mkfs.xfs read the mdraid configuration and configure 
the filesystem automatically for sw, swidth, number of allocation 
groups, etc.  Thus you should get max performance out of the gate.

If you really would like to fix this, you'll need to post on the XFS 
list.  Much more data will be required than simply stating "it's slower 
by x than 'raw' read".  This will include your mdadm config, testing 
methodology, and xfs_info output at minimum.  There is no simple "check 
this box" mega solution with XFS.

> Thank you for the suggestion though, I will have to book mark that link.

You're welcome.

You can't find a better value for an 8 port SAS or SATA solution that 
actually works well with Linux.  Not to my knowledge anyway.  You could 
buy two PCIe x1 4 port Marvell based SATA only cards for $20-30 less 
maybe, but would be limited to 500MB/s raw unidirectional PCIe b/w vs 
2GB/s with an x4 card, have less features, eat two slots, etc.  That 
would be more reliable than what you have now though.  The Marvell SATA 
driver in Linux is much more solid that the SAS driver, from what I've 
read anyway.  I've never used/owned any Marvell based cards.  If I go 
cheap I go Silicon Image.  It's too bad they don't have a 4 port PCIe 
ASIC in their line up.  The only 4 port chip they have is PCI based. 
Addonics sells a Silicon Image expander, but the total cost for a 2 port 
card and two expanders is quite a bit higher than the better Intel 
single card solution.

-- 
Stan