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Slow read speed on Areca ARC-8050

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pcamen

macrumors newbie
Original poster
Apr 9, 2014
2
0
I've got an Areca ARC-8050 thunderbolt (1) raid array set up with 8 4TB WD enterprise class hard drives, in RAID 6 mode. When I first tested it I was getting over 400 or 500 MB/s in both read and write speeds. Now, write speeds are still very fast but read speeds have degraded to around 90-150MB/s. I contacted Areca support and their suggestion is to delete and recreate the array, not a very good option as I've got 18TB of data on there now.

Anyone have any ideas as to why the read speed might have slowed down and what to do about it? I'm not incredibly familiar with all the settings you can change when setting up a RAID system like this; I pretty much went with the defaults the system offered.

This is attached to a late 2013 iMac.

I ran a disk verify through Disk Utility and it found no errors.
 
C

ColdCase

macrumors 68040
Feb 10, 2008
3,359
276
NH
I know just enough to be dangerous here but, if I recall correctly, when the RAID is in degraded mode for whatever reason, it doesn't take longer to write, but much longer to read. When in degraded mode, the RAID may not store data in "RAID" format with all the parity, its just stores the data. On the read side, it needs to recalculate and recover the data which takes much longer.

Disk utility is not going to detect errors, but the Areca RAID status utility may.

I'm sure someone will jump in here soon with a better answer.

Usually RAIDs go into degraded mode when there is a disk failure or integrity error. In this case recreating the RAID may be the only solution, unless the Areca utility specifies a drive with an issue. In that case, replacing the drive before rebuild may be prudent. From Areca's support reaction, I'm guessing they don't think its a drive.
 
Last edited:
P

pcamen

macrumors newbie
Original poster
Apr 9, 2014
2
0
ColdCase said:
I know just enough to be dangerous here but, if I recall correctly, when the RAID is in degraded mode for whatever reason, it doesn't take longer to write, but much longer to read. ...
Click to expand...

The Areca utility/status shows no issue with the RAID array. All disks are functioning perfectly and the status monitor shows no errors.
 
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