RAID 10 vs RAID 5 ?

What RAID level do you
recommend for a fileServer since
RAID 10 without a “hot spare” is almost always a
better choice than RAID 6 with a “hot spare” and
RAID 6 without a “hot spare” is always better
than RAID 5 with a “hot spare” ?
  ** PRO = can lose two drives
                = 50% to 88% Capacity Utilization
  ** CON = slow writes

  ** PRO = fast writes
  ** CON = can only lose one drive in each sub-array
                = 50% Capacity Utilization,
                   therefore more disk costs
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Nick RhodeIT DirectorCommented:
Do you prefer fault tolerance or speed?  If you want speed then go for raid 10

If you want fault tolerance it depends on how much you want?  Raid 5 only needs 3 disks and 1 can fail which means your still up and running, but if you lose 2 drives, well hopefully you have a backup.  Raid 6 is basically the same as 5 with not much of a speed difference between them but fault tolerance is better with a raid 6 but requires an extra drive.

So to summarize

Speed = go raid 10
Fault Tolerance = Raid 5
Fault Tolerance and you have money = Raid 6

Honestly if its just a file server where people will just be storing files, a Raid 5 should do just fine.  I typically do a raid 5 with a hotspare

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madunix (Fadi SODAH)Chief Information Security Officer Commented:
I would go Raid 5 for file server if read > write.
Carlos IjalbaIT Systems DirectorCommented:
Depending on your Needs:

-Normal File Server, with an average file use: RAID5

-Fast File Server, for example for a website that serves loads of PDFs or other small files: RAID10

-Slow File Server, like an ISO Repository, or to store backups: RAID6

From the 3 RAID groups offered here:
-The best Performance comes from RAID10, the worst from RAID6.
-The best resilience comes from RAID6, and the worst from RAID10.
-So RAID5 is bang on the middle and the best for an average solution.
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Jim_NimSenior EngineerCommented:
What size/capacity, interface type (SAS vs SATA) and spindle speed HDDs to you plan to use?
How many drives?
Are you planning on using software RAID or a hardware RAID controller?
What kind of I/O load does it need to support? (Is this replacing a solution that's already in place, with a measurable workload?)
How critical is the data?
How frequently will the data be backed up?

Each RAID type has a different performance impact, namely their write penalty (writes to RAID10 each require 2 IOs, RAID5 > 4 IOs, and RAID6 > 6 IOs).  You've already considered drive failure tolerance, but also keep in mind that RAID5 gets increasingly risky when you move toward high-capacity spindle drives. If you have 4TB drives, the chances of encountering a URE during a rebuild after a drive failure are high enough that RAID5 is typically no longer acceptable for storing production data. UREs result in permanently-lost RAID blocks/stripes that can cause data corruption, sometimes requiring a restore from backup to recover from.

Another thought... if your RAID implementation/solution allows for live RAID level conversions, you could likely start off with RAID10 and observe how well things perform. If you see that the usable capacity isn't going to be adequate, and you have some way of measuring the I/O load on the drives (or calculating it based on I/O against the RAID set as a whole, and comparing to the maximums your drives can handle based on average latency they're spec'd for) to ensure you've got IOPS to spare, then you could try migrating to RAID6.

A frequently-used middle ground to also consider is RAID50 - this splits your risk related to RAID5 in half (you can lose 1 drive in each of the two RAID5 sets without the RAID failing), gives you the same usable capacity as a RAID6 with the same number of drives, and without the hefty write penalty that comes along with RAID6.

Short answer:
High Write Performance + High Fault Tolerance Required: RAID10
Minimal Write Performance Required + Good Fault Tolerance: RAID6
Good Performance + Minimal Fault Tolerance Required = RAID5 or RAID50

Most usually settle for RAID5, thought the unlucky few end up reaping the repercussions of the higher risk.
Jim_NimSenior EngineerCommented:
You may also look at my answer on this post for a little more clarification about the differences between RAID10 and RAID6, regarding their tolerance against drive failures vs their susceptibility to UREs during rebuilds.
madunix (Fadi SODAH)Chief Information Security Officer Commented:
High Write Performance + High Fault Tolerance Required: RAID10
Minimal Write Performance Required + Good Fault Tolerance: RAID6
Good Performance + Minimal Fault Tolerance Required = RAID5
Gerald ConnollyCommented:
@financeteacher - RAID-5 only supports loss of ONE  drive.

And now that RAID-5 is not recommended with the current crop of very large drives (due to the risk of a second drive failing during the long rebuild times) it becomes a straight fight between RAID10 and RAID-6

RAID10 has the best performance but at only 50% utilisation
RAID-6 usually has much worse performance but better utilisation (min 50% with 4 drives, but 80% with 10 drives)
Dirk MareSystems Engineer (Acting IT Manager)Commented:

Performance over storage utilization for me personally. Drives are real cheap and losing half of the capacity is not a real issue for me.

Another thing to consider how much storage do you require and what are the limits of the device?

4 bay NAS
and you need +/- 18Tb usable storage
RAID 5 will be your answer as RAID10 would only give you 12Tb of usable storage.
calculated using 6Tb drives.

Sometimes your needs in relation to what you have would automatically give you your answer.

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