Messages in this thread | | | Date | Thu, 11 Mar 2010 20:07:29 +0100 | From | Matthias Schniedermeyer <> | Subject | Re: RAID + LUKS + LVM performance |
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On 11.03.2010 09:51, david@lang.hm wrote: > On Thu, 11 Mar 2010, Matthias Schniedermeyer wrote: > >> On 11.03.2010 13:08, Mathias Buren wrote: >>> >>> Hi, >>> >>> (please cc me as I'm not subscribed) >>> >>> I've a friend who's going to set up a fileserver consisting of 8x 1.5TB >>> HDDs, an 8-port PCI-E RAID card (Areca ARC-1220 @ >>> http://www.areca.com.tw/products/pcie.htm ) etc. >>> The plan is create a RAID5 array spanning all the disks, then create 4 >>> partitions. These 4 partitions would be encrypted using LUKS (Twofish or >>> AES256). >>> These 4 encrypted partition would be set up in RAID0 using Linux' software >>> (mdadm), then LVM would be used on top of that (one big PV, one big VG and >>> a big LV or so). >>> >>> The reason for this is that kcryptd is not multithreaded (afaik). By having >>> 4 encrypted partitions, then md0 on top of them, I'm forcing 4 kcryptd >>> processes to run on all four cpu cores whenever something is written to the >>> disks, which should improve (encryption) performance. >>> >>> Is this a good way of doing it, or is there a smarter way? >> >> The setup you describe would only work with SSDs. HDDs would seek >> themselves to death. >> >> The problem is the RAID-0 over the 4 partitions. At that point you would >> need, instead of the 4 partitions, something that is round-robin. So >> that the mapping of the (physical) blocks from the upper to the lower >> would be effectivly linear/unchanged. >> >> AFAIK something like that is (currently) not possible. > > linux software raid (the md tools) support linear or striped modes for > raid0, so what you are looking for is available.
Nope. What i meant is:
Let say you had a block-device which has 16 blocks: 0-15 With the OPs description the blocks would be distributed like this: Part 0: 00 01 02 03 Part 1: 04 05 06 07 Part 2: 08 09 10 11 Part 3: 12 13 14 15
What you need is a distribution like this: Device 0: 01 05 09 13 Device 1: 02 06 10 14 Device 2: 03 07 11 15 Device 3: 04 08 12 16
IOW: Blocks % 4 == 0 on device 0 Blocks % 4 == 1 on device 1 Blocks % 4 == 2 on device 2 Blocks % 4 == 3 on device 3
I still other words: You don't want a cake in exactly 4 same size parts. You want a cake in a million parts and then every 4th starting from the first piece in one set, every 4th starting from the second in the next and so on.
> however I think that defeats part of the OPs purpose, which was to try > and spread the I/O across all 4 partitions to be able to use multiple > cores for the encryption.
I think i just didn't make clear enough what i meant.
Bis denn
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