advice on expanding RAID10 array

I have a HP DL 380 G7 server populated with 12 146 gig 15k disks
2 disks have been configured RAID1 for c drive (136gig total) and 10 disks have been configured as RAID 10 array for D drive (684gig total)
I need to expand the D drive and have 4 bays left
is my only option to buy 4 x 146gig disks and add them to the existing RAID 10 array?
Can this be done online?
what storage would this add?
is it safe to add to existing array?
could I add larger disks to give more storage?
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andreasSystem AdminCommented:
It only can be done online if the particular raid controller in the machine allows extension of a raid 10 online.

it would add another 146 GB brutto (you will have some less free due to filesystem overhead)

it would NOT risk to do this online, without a valid, recent and working backup.
Online rebuilding this array will put a lot of stress to all the disks, and there are 6 disks in each stripe set that are together, if one disk break in each stripe set your files will be lost.
Although the disks are small so a rebuild would not take too long.

no you cant add bigger disks to that RAID 10 to get more space. A raid 10 is a mirror of 2 or more raid 0. in raid 0 you only gat as much space as the smallest disk in the stipe set has.
dougdogAuthor Commented:
so by adding 4 new 146 g disks what would my d volume be increased to?
andreasSystem AdminCommented:
ca. 820GB netto.
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dougdogAuthor Commented:
so I loose 3 disks and only gain 146gig space?
andreasSystem AdminCommented:
sorry you have 950 gb after adding 4 disks. Ive only calculated with 2 more.
dougdogAuthor Commented:
would it be better to add larger disks under a new array
David Johnson, CD, MVPRetiredCommented:
4 x 146gig disks and add them to the existing RAID 10 array
what you have now:
Capacity      876 GB
Speed gain      12x read and 6x write speed gain
Fault tolerance      At least 1-drive failure

What you will get:
Capacity      1168 GB
Speed gain      16x read and 8x write speed gain
Fault tolerance      At least 1-drive failure
Increase of 292GB
Raid Calculator
David Johnson, CD, MVPRetiredCommented:
adding larger disks only if you can do it but remember you are limited to the smallest disk size. Since you can only tolerate a 1 drive failure backup/backup/backup did I say backup..
dougdogAuthor Commented:
my d drive is only 684gig
David Johnson, CD, MVPRetiredCommented:
oops I thought you had 12 disks and increasing to 16 for the raid 10.. recalculated RAW capacity before formatting and other disk overhead.. Don't forget that drive manufacturers use *1000 and operating systems use *1024 so a 146GB drive really is 136.6GB

Capacity      685 GB
Speed gain      10x read and 5x write speed gain
Fault tolerance      At least 1-drive failure

Capacity      959 GB
Speed gain      14x read and 7x write speed gain
Fault tolerance      At least 1-drive failure

959 - 685 = 274 increase with adding 4 disks
dougdogAuthor Commented:
yes I have 12 disks in total 2 in RAID1 for OS
10 in RAID 10 for data
that's great many thanks
probably quite an expensive option just to get 274gig
dougdogAuthor Commented:
how do you know what to subtract for over head
14 x 146 gig = 1022 gig
but you say only 959 will be available
David Johnson, CD, MVPRetiredCommented:
Again HD manufacturers use base 10 units, Operating Systems use base 2 units.
1 MB = 1000 bytes (MFR) 1024bytes(O/S)
os reports approximately 97% of Mfr rating.  This is the unformatted RAW capacity. Therefor a 146 GB HD * .97 = 141.62 GB reported by the OS
a 1TB MFR = 970 GB (OS RAW) -> 931 GB formatted nfts default settings.

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dougdogAuthor Commented:
perfect thank you
andyalderStorage OwnerCommented:
>is my only option to buy 4 x 146gig disks and add them to the existing RAID 10 array?

No it isn't your only option. You could convert the current RAID 10 to RAID 6 on the fly* without adding any disks, that would give you 3 * 146 GB extra space although the write speed would only be half as fast as it is currently due to the RAID 6 write performance penalty. (take it as 3*136GiB usable extra given the GB/GiB difference.)

You would still have 4 spare bays so you could add a hot spare or two in them if you want or indeed add another 4 * 146GB disks' worth of space and a little more speed to the new RAID 6. That would compensate a bit for the RAID 6 write penalty as you would be adding more disk spindles which adds more speed.

*online RAID level conversion takes a day or so, a week if you set the expansion priority low on a heavily used server. just maintain your current backup regime. You may need to buy a cache battery or FBWC module to enable it, I don't think you need an expensive license for RAID 6 any more.
dougdogAuthor Commented:
its an oracle server so need the RAID 10 performance
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