M
markm75
With a 4 drive raid10.. i'm a little unclear on how many can fail here
and still work..
Same with 8 drive?
Any thoughts?
Thanks
and still work..
Same with 8 drive?
Any thoughts?
Thanks
raid10.. how many drives can fail and still have the array in tact?(4 drives/8 drives)
A
Arno Wagner
Previously markm75 said:
A raid 10 uses RAID1 components as basis to build a RAID 0 on
top. If in any of the RAID1 subcomponents two drives fail, the
whole array fails.
For 4 drives that would be two RAID1 pairs. If 1 drive fails,
the array works. If 2 drives fail, it may or may not work.
3 drives kill oit reliably.
That would be 4 RAID1 pairs.
1 drive failure will not kill it. 2-4 drive failures may or may
not kill it, depending on whcih drives fail. 5 drives reliably
kill the array.
Arno
M
markm75
So basically with 4 drive.. there are two on each side.. if 1 drive on
one side dies.. its ok.. but if 1 drive on each side dies then its a
goner.. if 2 drives fail on one side.. i'd think it would be ok, just
not mirrored..
I'm trying to decide for my beefy virtual hosting server and file
server what to do.. i have 8, 500gb drives..
i originally was going to do 4 drive raid 5 for the main filesharing/
shares area.. then raid10 4 drive, for the virtual servers being
hosted on this box (8 of them, only 3 remotely beefy i guess).. i'd
prefer an all in one solution, but that would mean either going 8
drive raid5 (which would be horribly slow on rebuilds) or 8 drive
raid10, which sounds a little risky but fast on writes.
A
Arno Wagner
You should determine what your bottlenecks are first. You
may even have time for RAID6 without knowing it.
Arno
M
markm75
Hi there..
What did you mean by that ...(bottlenecks)..
RAID6.. how many drives can fail here.. is it the same as raid5.. i
have forgotten.. i think there was extra parity?
So raid6, 8 drives of 500gb.. does this still equate to 3.5TB?
I didnt think the writes were any better with raid6 than raid5.. i've
always been a fan of the writes of raid10.
M
markm75
btw.. it took 10hr 37 min for my 4 drive (500gb each) raid5 set to
build on this card.. and it took 1hr 41 min for the raid10 4 drive set
to build.
M
markm75
From looking at this description.. it would appear that all but one
drive can fail on each side and the array still works?
http://en.wikipedia.org/wiki/Nested_RAID_levels#RAID_1.2B0 (so 4 on
each side, 3 can fail on each side in raid10)?
M
markm75
Btw.. forgot.. that 10hr build time was a background build, not
foreground and the raid10 time was foreground only.
A
Arno Wagner
Slowest components that matter.
RAID6 can survive loss of any two disks. Since parity is
not enough, it will be slow with two failed drives.
RAID6 is about good redundancy.
Arno
A
Arno Wagner
The RAID10 time is standard. The RAID5 time is extremely poor.
I have a 8 500GB disk software RAID6 on older hardware,
that builds in about 4 hours on Linux.
Arno
A
Arno Wagner
No. Example: If A1 and A1 fail, the whole array is broken.
A
Arno Wagner
What is a background build?
Arno
M
markm75
The build process is slower in a background build.. it gives the
option for initialization.. background or foreground.. but raid10
doesnt have this option.. you must stay in the bios (its not
immediately available).
I decided to do the 8 drive system for raid10.. i built it.. took the
same amount of time as 4 drives.. i then pulled 2 drives.. the drive
letter stayed in tact.. i pulled a 3rd drive.. it was then no longer
in tact..
So with 8 drives, it appears you can lose 2 and still be ok.. which is
the same as raid6.. so i think ill stick with raid10, since the 2tb
space is way more than we ever expected to have anyway (had 600gb
before
A
Arno Wagner
Previously markm75 said:
I see.
Depends on which drives you pulled.
So with 8 drives, it appears you can lose 2 and still be ok.. which is
the same as raid6.. so i think ill stick with raid10, since the 2tb
space is way more than we ever expected to have anyway (had 600gb
before
No, you cannot. Loose a RAID1 pair and the array goes down.
Arno
M
markm75
Ah crap.. i see that now.. did another random 2 drive test.. and
boom..
well.. i think i may opt to Not use raid10.. its quite sad, as the
performance i was getting using a performance tester was through the
roof.. i mean, we do use dpm 2007 to back stuff up, but this "chance"
of one going on each side is too hard to ignore..
I'm initializing an 8 drive raid6 array now, ill conduct the same
speed tests on it...
A
Arno Wagner
Pleas post results here. Could be interesting.
Arno
M
markm75
The initialization of an 8 drive raid6, only took 1hr 42 minutes
(foreground, not background).. same speed as the raid10 basically...
So here were my results.. these are from performance tester v6.1:
D: drive raid10, 8 drives,... (500gb, Seagate, 32mb cache, sataII, TOTAL
2.0TB space)
Burst speed of about 1050.4 MB/s
Avg read 351.2 MB/s
Seq writes of 235 MB/s (0.5x that of raid6?!)
Random seek+RW: 52.6 MB/sec (2.2x that of raid6)
D: drive raid6, 8 drive... (500gb, Seagate, 32mb cache, sataII, TOTAL
3.0TB space)
Burst speed of about 1049 MB/sec
Avg read 633 MB/sec !! (twice that of raid10)
D drive seq writes of 458.2 MB/sec (showing twice that of raid10??)
Random seek+RW: 18.0 MB/sec (random seek+RW, appears to be
slightly under half as fast as RAID10)
So it appears on random seek+RW, raid6 is the loser, but on sequential
writes.. its actually faster than RAID10, which seems odd to me..
Based on just these numbers (performance).. which would be the winner?
I always though raid10 should win...
But raid6 isnt horribly slower on a few specs, so i'm leaning towards
just sticking with RAID6?
All of these are with the ARC-1231ML Pci-e x8 card, which in my tests
shows faster stats than the 3ware comparative models.
A
Arno Wagner
Yes, these numberas are possible with RAID6, if you have a really
fast controller.
No, that is entriely correct. It is, after all, kind of a 6 way raid0.
As to the random RW, that is likely due to the writes being small,
but larger that the stripe size.
It used to be like that, because of limited computing power and bus
transfer speeds. As to raw disk access speeds RAID5/6 with
I think you should use RAID6.
Arno
D
David Lesher
RAID6 is RAID5 that survives two drive failures, not one.