# hot swap bays



## inwell (Sep 21, 2011)

help me understand the hot swap hdd bays present in pc cabinet .

1.do we need some diff. types of hdd ?

2. how these bays are connected to power and data ports ?


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## visseroth (Oct 25, 2010)

Hot swappable bays just indicate that the controllers in the machine allow for swapping out the hard drives while the machine is online. However one must keep in mind that any activity on that drive that gets pulled will cease and this will in turn affect the any applications or operating systems dependent on that drive.
Usually hot swappable bays are used for drives that are in an RAID array. For instance I have a Supermicro server with 12 hot swappable bays. The operating system is loaded from a compact flash card. All 12 drives are in a raid array which is setup to allow for 4 hard drive failures without corrupting the data. When I remove one drive the array goes into a degraded state but continues to function. When I replace that drive the operating system sees that I have inserted a new drive and gives me the option to rebuild my data back to the new drive there by giving me back my 4 drive redundancy.
This can be done with the operating system installed to array as well. For instance a RAID 5 with the OS installed to the array will allow for 1 hard drive failure without corrupting the data on the drives. The advantages to RAID 5 is 1 disc redundancy, larger storage pool being spread over 3+ discs and increased read speed. Disadvantage is the write speed is about as fast as having a single hard drive and increased overhead on the CPU due to the calculating of parity bits however this is also dependent on what kind of raid controller you have.

OK, so got off on a rabbit trail, sorry about that. To answer your questions more specifically.....

1. A: This depends on the machine. Some hot swappable machines use SCSI (See this page as it seems to give some good info... Identify SCSI HD at a glance ) and some use Serial attached SCSI (See this page Serial attached SCSI - Wikipedia, the free encyclopedia ) which most of the time is backwards compatible with SATA. In my case my server has Serial attached SCSI bays (AKA SAS) but I have 12 2TB 5900RPM SATA hard drives in it.
So Basic answer is sometimes yes, anymore not really but check with your manufacturer.

2. A: There are connectors at the back of the bays that interface with the hard drive when they are slid in. Usually these are known as backplanes (See these images to see various backplanes https://www.google.com/search?q=har...v&sa=X&ei=096cUNuhNOLniwKtmoGgDA&ved=0CG0QsAQ ). These interfaces connect to the power and data interface of the hard drives.

I hope this answers your questions.


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## inwell (Sep 21, 2011)

thanks for the info. 

my actual query was the connectivity. so by the images u linked , can i say that he tower supporting hotswap bays comes pre wired and we just need to place hdd in that tray (making sure it is connected/inserted in the tray properly making the needed contact )


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## visseroth (Oct 25, 2010)

Indeed that is the case.


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## JimE (Apr 16, 2009)

You can add removable bays to any PC. The data (ie: IDE or SATA) and power connections are the same as with any other HDD or CD/DVD drive that you would install.


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## inwell (Sep 21, 2011)

@ Dogg

so these bays /trays supporting more than two HDDs have a power supply in common ? how actually this thing work ? (connectors from PSU are quite limited )


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## visseroth (Oct 25, 2010)

The power is shared and split to each drive in series.


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## JimE (Apr 16, 2009)

It varies by the brand/model of the bay. In most instances, a power cable is needed for each drive supported. The only exception that I've seen are the 5n3 bays, which use only four.

If you don't have enough power connectors, then you also need to upgrade the power supply.


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