gjournal+gstripe+gmirror question

[Ivan Voras]

Alexei Troussov wrote:
> Hello All,
> 
> I decided to build multi-terabyte data storage (file server) using 4 x
> 1Tb disks. No special raid controller is used, FreeBSD 7.1 is running on
> another disk, so the disk array is going to be used for file storage only.
> So, I tried several combinations of gmirror/gstripe and put gjournal on it:
> 
> 1) two mirrors and stripe on them

This is RAID 10

> 2) two stripes and mirror on them

This is RAID 01. It is slightly worse because if one drive fails, no
other drive must be allowed to fail. In the RAID10 case, each drive from
the mirrored sets can fail.

> Both configurations gave excellent I/O speed (around 100Mb/sec), and I

You should get better - the total performance should be near or even
slightly above 2-drive striped (RAID-0) configuration. Modern drives
have sequential performance between 60 MB/s and 80 MB/s so you should be
getting between 120 MB/s and 160 MB/s.

> chose the first one as it needs less time to resync disks when one of
> the mirrors fails. To make picture more complete, I didn't try graid3
> because it seems to load CPU more than configs above, which is not good
> for my barebone :)

Correct.

> Now when my top-level gstripe gets "gjournal"-ed, I see relatively poor
> write speed around 20-30 Mb/sec.
> As far as I understand from man gjournal and some posts here,
> performance usually drops about 40-50%, but what I have is much worse...
> 
> Are there a better way to configure/tune the whole thing?
> Thanks in advance!
> 
> PS Here is my current playground config:

> Stripesize: 131072

Try a stripe size of 16 kB.

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 258 bytes
Desc: OpenPGP digital signature
Url : http://lists.freebsd.org/pipermail/freebsd-geom/attachments/20090521/70f2a0e4/signature.pgp