On Fri, 12 Dec 2008, Brad Campbell wrote:
Ryan Wagoner wrote:
It takes 3 hours to resync my 3 x 1 TB drive RAID 5 array at a rate of
85MB/s. It shouldn't take 20 hours to write 3 x 1 TB drives. How fast
is it progressing? You might consider a PCI-X or PCI Express SATA or
SAS controller card. I have my drives connected to an Supermicro LSI
1068 PCI Express SAS card, which performs great.
I'm using 2 x Marvell 7042 based PCI-E x4 controllers and a SIL 3xxx (I don't
recall but its PCI-E x1 and 2 ports). Bandwidth is not an issue.
A resync appears to be a completely different kettle of fish to a reshape.
With re-shape it appears to write status data to the raid superblocks
periodically. This appears to thrash the heads from the current position to
the end of the disk and back. At the start of the reshape I was running about
15-20MB/s to each drive. As the reshape progressed to the end of the disks I
was looking at closer to 40MB/s. So obviously the final figure was less than
the initial 20 hours, but a hell of a lot slower than a straight resync.
This blind stab at reshape behaviour is absolutely pure conjecture based on a
gross guess at what was happening, however it does seem to bear out scrutiny.
The other option would be to create 2 RAID 5 arrays of 5 drives each.
Create the first array and use LVM with the filesystem of your choice.
Add the second array later and expand the LVM volume.
Mmm thanks, but no.. to use a car analogy, "I'd like something I can fix with
a screwdriver and a hammer". LVM is overcomplicating things way past what I
require. In addition, I really like RAID-6. Over the last 4 years with my 15
drive RAID-6 I have had two double drive failures. Both times one drive died
in a not so nice fashion, and one developed a grown defect during the
rebuild. Raid-5 just does not cut the mustard with me anymore.
^^^^^^^^^^^^^
Agree with you there, even when you have the data backed up losing and
having to rebuild everything is such a pain-- RAID-6 has served me quite
well and I have only started using it recently, it did save me from one
double-drive failure so far, I have not looked back since.
Justin.
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