Hi Mark,
What would be really useful here is a description of what you actually
/want/. What do you want to do with these drives? What sort of files
are they - big or small? Do you need fast access for large files? Do
you need fast access for many files in parallel? How important is the
data? How important is uptime? What sort of backups do you have? What
will the future be like - are you making one big system to last for the
foreseeable future, or do you need something that can easily be
expanded? Are you looking for "fun, interesting and modern" or "boring
but well-tested" solutions?
Then you need to make a list of the hardware you have, or the budget for
new hardware.
Without know at least roughly what you are looking for, it's easy to end
up with expensive SSDs because they are "cool", even though you might
get more speed for your money with a couple of slow rust disks and a bit
more ram in your system. It may be that there is no need for any sort
of raid at all - perhaps one big main disk is fine, and the rest of the
money spent on a backup disk (possibly external) with rsync'd copies of
your data. This would mean longer downtime if your main disk failed -
but it also gives some protection against user error.
And perhaps btrfs with raid1 would be the best choice.
A raid10,f2 is often the best choice for desktops or workstations with 2
or 3 hard disks, but it is not necessarily /the/ best choice.
mvh.,
David
On 01/06/14 16:25, Mark Knecht wrote:
Hi Craig,
Responding to both you and David Brown. Thanks for your ideas.
- Mark
On Sat, May 31, 2014 at 9:40 AM, Craig Curtin <craigc@xxxxxxxxxxxxx> wrote:
It sounds like the op has additional data ports on his MOBO - wouldn't he be
better off looking at a couple of SSDs in raid 1 for his OS, swap etc and
his VMs and then leave the rest for data as raid5 - By moving the things
from the existing drives he gets back space and only purchases a couple of
good sized fast SSDs now
It's a possibility. I can get 240GB SSDs in the $120 range so that's
$240 for RAID1. If I take the five existing 500GB drives and
reconfigure for RAID5 that's 2TB. Overall it's not bad going from
1.4TB to about 2.2TB but being it's not all one big disk I'll likely
never use it all as efficiently. Still, it's an option.
I do in fact have extra ports:
c2RAID6 ~ # lspci | grep SATA
00:1f.2 IDE interface: Intel Corporation 82801JI (ICH10 Family) 4 port
SATA IDE Controller #1
00:1f.5 IDE interface: Intel Corporation 82801JI (ICH10 Family) 2 port
SATA IDE Controller #2
03:00.0 SATA controller: Marvell Technology Group Ltd. 88SE9123 PCIe
SATA 6.0 Gb/s controller (rev 11)
06:00.0 SATA controller: JMicron Technology Corp. JMB363 SATA/IDE
Controller (rev 03)
06:00.1 IDE interface: JMicron Technology Corp. JMB363 SATA/IDE
Controller (rev 03)
c2RAID6 ~ #
Currently my 5-drive RAID6 uses 5 of the Intel ports. The 6th port
goes to the CD/DVD drive. Some time ago I bought the SATA3 Marvell
card and a smaller (120GB) SSD. I put Gentoo on it and played around a
bit but I've never really used it day-to-day. Part of my 2-drive RAID1
thinking was that I could build the new RAID1 on the SATA3 controller
not even touch the existing RAID6. If it works reliably on that
controller I'd be done and have 3TB.
I think David's RAID10 3-drive solution could possibly work if I buy 3
of the lower cost new WD drives. I'll need to think about that. Not
sure.
Thanks,
Mark
On Sat, May 31, 2014 at 9:40 AM, Craig Curtin <craigc@xxxxxxxxxxxxx> wrote:
It sounds like the op has additional data ports on his MOBO - wouldn't he be
better off looking at a couple of SSDs in raid 1 for his OS, swap etc and
his VMs and then leave the rest for data as raid5 - By moving the things
from the existing drives he gets back space and only purchases a couple of
good sized fast SSDs now
Sent from my Samsung tablet
.
-------- Original message --------
From: David Brown
Date:31/05/2014 21:01 (GMT+10:00)
To: Mark Knecht ,"L.M.J"
Cc: Linux-RAID
Subject: Re: Home desktop/server RAID upgrade
On 30/05/14 22:14, Mark Knecht wrote:
On Fri, May 30, 2014 at 12:29 PM, L.M.J <linuxmasterjedi@xxxxxxx>
wrote:
Le Fri, 30 May 2014 12:04:07 -0700, Mark Knecht
<markknecht@xxxxxxxxx> a écrit :
In a RAID1 would a 3-drive Red RAID1 possibly be faster than the
2-drive Se RAID1 and at the same time give me more safety?
Just a question inside the question : how do you manager a RAID1
with 3 drives ? Maybe you're talking about RAID5 then ?
OK, I'm no RAID expert but RAID1 is just drives in parallel right. 2
drives, 3 drives, 4 drives, all holding exactly the same data. In
the case of a 3-drive RAID1 - if there is such a beast - I could
safely lose 2 drives. You ask a reasonable question though as maybe
the way this is actually done is 2 drives + a hot spare in the box
that gets sync'ed if and only if one drive fails. Not sure and maybe
I'm totally wrong about that.
A 3-drive RAID5 would be 2 drives in series - in this case making
6TB - and then the 3rd drive being the redundancy. In the case of a
3-drive RAID5 I could safely lose 1 drive.
In my case I don't need more than 3TB, so an option would be a
3-drive RAID5 made out of 2TB drives which would give me 4TB but I
don't need the space as much as I want the redundancy and I think
RAID5 is slower than RAID1. Additionally some more mdadm RAID
knowledgeable people on other lists say Linux mdadm RAID1 would be
faster as it will get data from more than one drive at a time. (Or
possibly get data from which ever drive returns it the fastest. Not
sure.)
I believe one good option if I wanted 4 physical drives would be
RAID10 but that's getting more complicated again which I didn't
really want to do.
So maybe it is just 2 drives and the 3 drive version isn't even a
possibility? Could be.
With 3 drives, you have several possibilities.
Raid5 makes "stripes" across the three drives, with 2 parts holding data
and one part holding parity to provide redundancy.
Raid1 is commonly called "mirroring", because you get the same data on
each disk. md raid has no problem making a 3-way mirror, so that each
disk is identical. This gives you excellent redundancy, and you can
make three different reads in parallel - but writes have to go to each
disk, which can be a little slower than using 2 disks. It's not often
that people need that level of redundancy.
Another option with md raid is the raid10 setups. For many uses, the
fastest arrangement is raid10,f2. This means there is two copies of all
your data (f3 would be three copies), with a "far" layout.
<http://en.wikipedia.org/wiki/Linux_MD_RAID_10#LINUX-MD-RAID-10>
With this arrangement, reads are striped across all three disks, which
is fast for large reads. Small reads can be handled in parallel. Most
reads while be handled from the outer half of the disk, which is faster
and needs less head movement - so reading is on average faster than a
raid0 on the same disks. Small writes are fast, but large writes
require quite a bit of head movement to get everything written twice to
different parts of the disks.
The "best" option always depends on your needs - how you want to access
your files. A layout geared to fast striped reads of large files will
be poorer for parallel small writes, and vice versa. raid10,f2 is often
the best choice for a desktop or small system - but it is not very
flexible if you later want to add new disks or replace the disks with
bigger ones.
md raid is flexible enough that it will even let you make a 3 disk raid6
array if you want - but a 3-way raid1 mirror will give you the same disk
space and much better performance.
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