I am just putting together my first unraid build. I understand the limit is 16 drives, but does this include the parity and cache drives?

What if I use the motherboard RAID to create a RAID0 volume for cache, would this be counted by unraid as one drive or two? And, more importantly, would that improve performance?

 

Luca

I am just putting together my first unraid build. I understand the limit is 16 drives, but does this include the parity and cache drives?

What if I use the motherboard RAID to create a RAID0 volume for cache, would this be counted by unraid as one drive or two? And, more importantly, would that improve performance?

 

Luca

The cache drive is not included in that number.  The parity drive is.  You can have 15 data drives.

 

A cache drive helps in the apparent "write" speed to the array at the expense of not having RAID protection of its contents until they are moved to the protected array (typically in the middle of the night)

 

Typically you can write to the cache drive two to three times faster than to the protected array. 

See here in the wiki

http://lime-technology.com/wiki/index.php?title=FAQ#What_is_the_difference_between_the_unRAID_licenses.3F

http://lime-technology.com/wiki/index.php?title=User_Benchmarks

http://lime-technology.com/wiki/index.php?title=FAQ#How_fast_is_unRAID.3F

 

Joe L.

The cache drive is not included in that number.  The parity drive is.  You can have 15 data drives.

 

A cache drive helps in the apparent "write" speed to the array at the expense of not having RAID protection of its contents until they are moved to the protected array (typically in the middle of the night)

 

Typically you can write to the cache drive two to three times faster than to the protected array. 

 

Joe L.

 

Thanks. Definitely useful then.    Would RAID0 would be a good choice for a cache volume?

Thanks. Definitely useful then.    Would RAID0 would be a good choice for a cache volume?

 

There is little benefit provided by having the cache drive in a RAID 0 configuration.

Typically, if you purchase a fast enough cache drive, they network is the bottleneck.

 

Besides, a raid0/raid1 arrangement can only be achived using a silicon image hardware right now.

Example: http://www.addonics.com/products/host_controller/ad2sahpmeu.asp

 

Now if you used this SIL5744 chipset in a SAFE50 or SAFE33 environment you could have a spanned parity drive and raid1 cache drive using two drives.

This post has more links regarding hardware raid using a port multiplier.  It has been reported that spin-down when idle does not work when RAID1 drives are behind a port multiplier.

 

http://lime-technology.com/forum/index.php?topic=4319.msg39079#msg39079

This post has more links regarding hardware raid using a port multiplier.   It has been reported that spin-down when idle does not work when RAID1 drives are behind a port multiplier.

 

http://lime-technology.com/forum/index.php?topic=4319.msg39079#msg39079

 

If the drives are set up with anything other then JBOD, they will not spin down.

I've tested this and it is a known factor

 

For someone like me where the parity drive is always spinning (because of my rtorrent client) it does not really matter.

Thanks. Definitely useful then.    Would RAID0 would be a good choice for a cache volume?

 

There is little benefit provided by having the cache drive in a RAID 0 configuration.

Typically, if you purchase a fast enough cache drive, they network is the bottleneck.

 

Besides, a raid0/raid1 arrangement can only be achived using a silicon image hardware right now.

Example: http://www.addonics.com/products/host_controller/ad2sahpmeu.asp

 

Now if you used this SIL5744 chipset in a SAFE50 or SAFE33 environment you could have a spanned parity drive and raid1 cache drive using two drives.

 

I was thinking of using one WD 640 black for the cache drive (WD6401AALS). If RAID0 would only double the chances of failure, without providing much benefit, I'm going to pass on that. The file transfers will be mostly from an existing RAID5 array, switches are all 1000.  Interesting info about the SIL5754, I did not know that. Though I think I am sticking with the hardware I've bought this time around, maybe for the next build. 

I only had a few hours to play with unRAID. All the hardware got recognized right away, installed preclear and unmenu. Everything works, where is the challenge??  Thanks for all the support you guys provide. I'd like to post a build thread with some pics a little later.

 

Luca

maybe he meant RAID1?

 

maybe he meant RAID1?

 

RAID1 will not spin down either.

Where this chipset would help is in a SAFE50 or SAFE33 environment where 2 drives are divided.

 

part of the two drives are RAID0 giving a large virtual drive for Parity.

part of the two drives are RAID1 giving a smaller, redundant virtual drive for cache.

 

Neither of the hardware drives will spin down on command.

Again, if you have a busy system like mine, it would not matter as they would always be spinning anyway.