Re: [Moosefs-users] Raid for Chunkserver?

[Michal B. <mic...@ge...>]

Hi!

We at Gemius do not use any RAID as we do not see any real profit in it.
Here are some of our thoughts on the subject:
- stability: if one disk fails it doesn't mean the whole chunkserver is
disconnected; chunkserver monitors the disks and just disconnect the broken
one
- less disks: by raid5, yes, by raid10 no; raid10 + goal=2 would be the same
as separate disks and goal=4 - but do you need security as goal=4? Probably
not and goal=3 and separate disks will demand less disks. And it is better
to have data spread over three computers than over two. 
- speed: one would need to do detailed tests; as for individual operations
for read/write RAID for sure would be quicker, but when talking about a real
life environment which is heavily used, we are not sure about the RAID
performance.


Kind regards
Michał Borychowski 
MooseFS Support Manager
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Gemius S.A.
ul. Wołoska 7, 02-672 Warszawa
Budynek MARS, klatka D
Tel.: +4822 874-41-00
Fax : +4822 874-41-01




-----Original Message-----
From: wk...@bn... [mailto:wk...@bn...] 
Sent: Wednesday, May 11, 2011 7:26 AM
To: moo...@li...
Subject: [Moosefs-users] Raid for Chunkserver?

Greetings:

We are testing MFS and have been very impressed so far.

One discussion that we are having internally is the desireability to use 
RAID (either Raid0, Raid1 or Raid10) on chunkservers.

Obviously with a goal of 2 or more, its not a protection issue, which is 
the classic RAID scenario.

as we see it, RAID on chunkservers has the following to recommend it.

+ stability:  Assuming RAID1/10, if a drive dies the chunkserver doesn't 
immediately fall out of the cluster, and forcing a need to rebalance. We 
can fail it deliberately at a time of our choosing to replace the drive.
+ less disks: with RAID1/10 we might feel better using a goal of 2 
instead of 3.
+ speed: RAID0 would be faster outright. RAID1/10 may provide faster on 
reads and slightly slower on writes (RAID 10 much better).

The reasons against would be:

- stability: with RAID0, the loss of a single drive kills the entire 
chunkserver.
- stability: another layer to fail (the MD layer).
- cost: increased power consumption and of course 2x or more the number 
of drives. We would be using Linux SoftRaid (MD driver) rather
than hardware raid, so the card cost is not an issue.
- speed: slightly slower writes on RAID1/10

So what is the consensus of the more experienced users?

Are you using RAID (0,1,10 or others) on your chunkservers?

Are we missing something on the above analysis?

-bill




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