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Cache Drive and Performance


Guest patm95

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Guest patm95

Hi all. I am building a server as we speak and I am interested in installing sabnzbd and sickbeard on it.  I am wondering though if I should put a cache drive in it?  I realize that a cache drive will help increase the performance, but is that the only real advantage?  How much of a performance boost is it?  Does it only effect the performance of the drive that it is installed on or all drives in general?  Thanks!

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one thing about the cache drive is it is unprotected so that is were the performance increase comes from. What I do is put my torrents/newsgroups on the cache drive then I verify that I like what I got then I put it into its proper drive. for example I split things into multiple drives so 1 drive for dvd's another for blu-ray, another for tv, games,ect. I haven't tested it out but my hope is it will increase performance when I do stream stuff, I can watch a blu-ray while my gf catches up on jersey shore(can't believe I agreed to set this up to get this show)

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Jersey Shore... sounds like a prime candidate for Targeted Media Failure.

 

The cache drive also helps to reduce fragmentation. Since news, torrents & such mean lots of file creation, assembly, and deletion, letting them do their thing in temporary space (the cache) before being copied to the array when finished reduces the churn on your main filesystems.

 

Give it a try. I initially used an ancient 80GB drive for cache that wasn't faster than my array of 1 and 2TB drives. Later I upgraded to a faster 320GB, but it ran very hot. Finally installed a 1TB "Black" cache drive and now my cache writes are twice as fast as those to my array. Definitely helps when joining, extracting, etc.

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Hi all. I am building a server as we speak and I am interested in installing sabnzbd and sickbeard on it.  I am wondering though if I should put a cache drive in it?  I realize that a cache drive will help increase the performance, but is that the only real advantage?  How much of a performance boost is it?  Does it only effect the performance of the drive that it is installed on or all drives in general?  Thanks!

The "cache" drive does absolutely nothing to improve the read speed of the array, in fact, if anything, it probably slows it a very tiny bit.

 

It was introduced to assist in the apparent "write" speed to the array back when you could only write to the array at 10MB/s or less..  Today, with improvements to the linux kernel and unRAID write speeds of 25 to 30 MB/s are common with modern hardware and 7200 RPM disks.

 

A cache drive allows you to write to the unRAID array at speeds approaching 80 MB/s. It does this by allowing you to write to an unprotected "temporary" disk (known as the cache disk), and subsequently, in the middle of the night copies the unprotected file to the protected array.  This occurs at the usual 20 to 35 MB/s, but since you do not experience the slower speed in the initial copy, you think performance is improved.  Until the file is copied, it is entirely unprotected from a disk failure.

 

 

 

 

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Don't run SAB and Sick but I do have all my torrents on the cache drive. It allows me to sift through everything first and then transfer to the array. Also I copy directly to the array so the cache drive is actually disabled for writes.

 

I use a cache drive as for the torrents it is the drive spinning all the time and also a a spare to go.

 

Josh

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I've tried cache disk twice; once with an old 250gb IDE disk, and then again with a 1tb WD FALS disk. Interface was master IDE slot and PCI. I installed sab on both and it functioned without any error. My only difficulty was with transfer speeds. As follows:

 

IDE sab download directory to cache share: 12-15 kbytes/s

IDE sab download directory to share (cache disabled): 20-25 kbytes/s

SATA sab download directory to cache share: 15-20 kbytes/s

SATA sab download directory to share (cache disabled): 25-30 kbytes/s

 

From my machine directly to the array (parity being written): 30-40 kbyte/s

 

I love sab and continue to use it, but on my desktop. The extra time for transfers annoyed me, so I converted that disk back into data storage.

 

Also, I think a lot of the time, Python would not properly shut down. That required a powerdown command via Putty. Scary. Sometimes the user script for python shutdown worked, sometimes not. I never did figure it out. So many variables.

 

 

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