A question about X-RAID

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kamanwu wrote:

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I was heard raid 5 is outdated. The perfermance is NOT good (compare with raid 1).  Also, becase of the way it works, there is a high chance 2 disk have issue at the same time.  (Is that true?)

 

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The RAID mode doesn't increase the chances of two disks having problems at the same time.  And either way, you can lose data if two disks fail.  Though with two RAID-1 groups, there is protection against some two disk failures (in your proposal, one 3 TB and one 8 TB drive could fail with no loss).

 

Read performance on large files should be the same with RAID-5.  Write performance can be a bit slower due to the need to update the parity blocks.  With small files, the limit is usually the iops - which is fundamental to all mechanical disks.  The best way to increase performance there is to use SSDs.

 

But with a home NAS, the performance is usually limited by the gigabit network speed - not by the disk or RAID speeds.  It's quite different with enterprise servers and data centers - which either have the storage in the server itself or are using much faster networks (up to 100 gb/s).

 

FWIW, three of own NAS use XRAID/RAID-5 - volume sizes range from 20 to 30 TB.

 

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kamanwu wrote:

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Here is the post I read: https://community.spiceworks.com/topic/545782-raid-5-unsafe-where-is-the-proof 

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FWIW, I agree with the "where is the proof" comments. I don't find arguments based on URE statistics convincing - they generally take the URE specs in the drive datasheets as reality (which in my experience they aren't - I've seen very few UREs).  The older articles suggest that I shouldn't be able to do a resync on arrays the size I am running now - but I haven't had them fail. I also run quarterly scrubs - which are also essentially resyncs - and I haven't had issues with them either. 

 

That said, disks (and devices) do fail - and sometimes it can take a while for bad sectors on a disk to be detected (since in most cases there is a lot of data that isn't accessed all that often).  So you do need to have a back up plan in place for your NAS, no matter what RAID mode you use.  I also recommend using the maintenance schedule (on the volume tab) to periodically test the disks.  Personally I run one of the maintenance functions every month (cycling through all four 3 times a year).

 

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kamanwu wrote:

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 I prefer ONE volumn which is 11T.  

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Which amounts to RAID-10.

 

I haven't tried converting RAID-1 to RAID-10 manually with FlexRAID, but I think you can create a RAID-1 group on the larger disks, and concatenate it to the existing volume. 

 

You could also switch to FlexRAID, uninstall your apps, delete the volume, and create a new RAID-10 volume.  You'd need to reconfigure the NAS, reinstall the apps, and restore the data from backup.

 

Personally I think the main attraction of two RAID-1 volumes is that RAID recovery (if you ever need it) is much easier.  

 

In practice, there isn't much difference between two volumes and one when you are accessing the NAS with SMB.  Either way, you just see the list of shares when you access the NAS over the network.  You do need to roughly balance the storage, so you keep adequate free space on both volumes.  That would need some occasional adjustments (moving some shares or folders around).