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| howa... |
 Posted: Fri Apr 24, 2009 7:56 am |
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Guest
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Hello,
We have just bought Dell MD1000, together with 15 SAS 15K hard disks.
This server will be connected to 6 web servers which provide a
centralized storage using NFS.
This server is important as if it down, other web servers didn't work
so I need to consider if which Raid configuration is better choice?
Assume it is 80% rad, 20% write, and average file size is around
30-50KB. Total capactity is important so we don't consider RAID 10.
Should I set RAID50 for my server? Or Raid6?
Thanks. |
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| Posted: Fri Apr 24, 2009 10:33 am |
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Guest
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howa <howachen at (no spam) gmail.com> kenjka:
Quote: We have just bought Dell MD1000, together with 15 SAS 15K hard disks.
This server will be connected to 6 web servers which provide a
centralized storage using NFS.
This server is important as if it down, other web servers didn't work
so I need to consider if which Raid configuration is better choice?
Assume it is 80% rad, 20% write, and average file size is around
30-50KB. Total capactity is important so we don't consider RAID 10.
Quote: Should I set RAID50 for my server? Or Raid6?
RAID5 would be much better (14 drives + 1 hotspare)... RAID6 is for big
capacity drives mostly...
--
"Slomljens li Srbinu izdrkavu ?" upita Marisol njusi Ficoog mrcvarija.
"Ne znam ja nista !" rece crijevoo podmazuje "Ja samo kruskao kolje Madjarskim !"
By runf
Damir Lukic, calypso at (no spam) _MAKNIOVO_fly.srk.fer.hr
http://inovator.blog.hr
http://calypso-innovations.blogspot.com/ |
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| Bill Todd... |
| Posted: Fri Apr 24, 2009 4:06 pm |
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Guest
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howa wrote:
Quote: Hello,
We have just bought Dell MD1000, together with 15 SAS 15K hard disks.
This server will be connected to 6 web servers which provide a
centralized storage using NFS.
This server is important as if it down, other web servers didn't work
so I need to consider if which Raid configuration is better choice?
Assume it is 80% rad, 20% write, and average file size is around
30-50KB. Total capactity is important so we don't consider RAID 10.
Should I set RAID50 for my server? Or Raid6?
Well, you could back up and reconsider your purchase decision, since you
could quite possibly get higher capacity, better performance, and better
availability at lower cost using (more) SATA drives in RAID-10.
Assuming that's not an option, then if availability is as important as
you suggest RAID-6 might be best - especially if the hardware will shut
down the RAID-5 array if a disk fails and it encounters a bad sector
while rebuilding (I've never understood why arrays would do this rather
than just report the bad sector and continue, just as would happen with
an individual disk, but many apparently do).
- bill |
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| howa... |
| Posted: Fri Apr 24, 2009 4:18 pm |
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Guest
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Hello,
On Apr 24, 8:06 pm, Bill Todd <billt... at (no spam) metrocast.net> wrote:
Quote: howa wrote:
Assuming that's not an option, then if availability is as important as
you suggest RAID-6 might be best - especially if the hardware will shut
down the RAID-5 array if a disk fails and it encounters a bad sector
while rebuilding (I've never understood why arrays would do this rather
than just report the bad sector and continue, just as would happen with
an individual disk, but many apparently do).
- bill
Well, how about Raid 50?
I read some of the posts in this group and seems people don't like it
very much? |
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| Posted: Fri Apr 24, 2009 6:33 pm |
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Guest
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howa <howachen at (no spam) gmail.com> kenjka:
Quote: Assuming that's not an option, then if availability is as important as
you suggest RAID-6 might be best - especially if the hardware will shut
down the RAID-5 array if a disk fails and it encounters a bad sector
while rebuilding (I've never understood why arrays would do this rather
than just report the bad sector and continue, just as would happen with
an individual disk, but many apparently do).
Well, how about Raid 50?
I read some of the posts in this group and seems people don't like it
very much?
Fast as RAID5, capacity loss like RAID6 (N-2 drives are used for
capacity)... Better go with RAID6 without complications...
--
Balkona pjeva optuzen u pilotskoj kabini kondomo podriguje
navecer ? By runf
Damir Lukic, calypso at (no spam) _MAKNIOVO_fly.srk.fer.hr
http://inovator.blog.hr
http://calypso-innovations.blogspot.com/ |
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| Bill Todd... |
| Posted: Fri Apr 24, 2009 11:48 pm |
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Guest
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howa wrote:
Quote: Hello,
On Apr 24, 8:06 pm, Bill Todd <billt... at (no spam) metrocast.net> wrote:
howa wrote:
Assuming that's not an option, then if availability is as important as
you suggest RAID-6 might be best - especially if the hardware will shut
down the RAID-5 array if a disk fails and it encounters a bad sector
while rebuilding (I've never understood why arrays would do this rather
than just report the bad sector and continue, just as would happen with
an individual disk, but many apparently do).
- bill
Well, how about Raid 50?
RAID-50 shares the basic failure characteristics of RAID-5: it's just 2
or more RAID-5 arrays bound together with RAID-0-style striping on top.
This does lower (but not dramatically) the probability that a bad
sector will be found during a rebuild after a disk fails (or that a
second disk in the same RAID-5 group will fail before the rebuild
completes) - and if either occurs your system still becomes unavailable
(unless the array can tolerate finding a bad sector during rebuild).
RAID-50 also tends to mitigate the performance hit that the system takes
before a failed disk has been replaced and rebuilt.
IMO RAID-50 is a good solution if the array logic will permit a rebuild
to complete even if a bad sector is encountered, because that's by far
the major threat with today's disk sizes: as long as there aren't too
many disks in each group the likelihood of a second whole-disk failure
within that group before a rebuild completes is pretty small, and
RAID-50 lets you limit the RAID-5 group sizes to a reasonable value
(say, under 10) that still gives you good space efficiency. Of course,
that will still leave you with a potentially unavailable file (unless
the bad sector happens to be in free space), so you'll need to find out
where it is and then rewrite the file (e.g., from a backup copy) to make
it fully-accessible again.
- bill |
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