Re: SAME methodology questions...

I have no experience, but I am also curious about how others are doing this after recently reading about this because there are more people (in our company) recommending SAME.

Sorry if I am creating a discussion you didn't want, but I would like to also hear from those who use SAME to explain a couple of things about their setup.

SAME is suppose to "keep it simple" . It seems it does IF you configure the disks correctly, but the 1 thing I would still worry about is not multiplexing REDO to 2 different sets of disk spindles. Does anyone using SAME have a good explaination why this is not potentially a problem.

Also, there are a couple of little details like the 1M stripe size and "using the outer edges of the disk platter for frequently accessed files" , that are not so simple. Our SysAdmin didn't have any idea how to do the outer edges setup on Sun A1000 arrays. Does SAME require specific/expensive hardware?

-- 

"Ron Bergeron" <bergeror_at_asitshouldbe.com> wrote in message
news:E2yEa.86017$DV.100771_at_rwcrnsc52.ops.asp.att.net...


> I've been reading about the SAME (Stripe And Mirror Everything)

> methodology recently. I understand the basic concept and the claim as to

> why it is a Good Thing. However, I'm unclear as to the actual

> implementation of it, especially in cases where a hardware RAID array is

> involved.

>

> The things I've read say to use a 1 MB stripe depth and 1 MB I/O size to

> stripe across as many physical spindles as possible. Mirror everything

> to another set of disks. 1 MB of data would be written to a disk before

> moving on to the next disk. That concept is simple enough.

>

> Assume I'm in a Sun/Veritas/EMC (Clariion)/Oracle environment.

>

> The Clariion has a limitation of striping across a maximum of 8 disks

> while at the same time mirroring to another set of 8 disks (RAID 1+0).

> (It can do a stripe across 16 disks, but to both stripe and mirror, it

> can only go 8 disks wide). For manageability, I'd prefer to strip across

> sets of 4 disks and mirror to another 4 disks. (More on this later.)

>

> To increase the number of physical spindles, I want to set up several of

> these 4+4 disk RAID 1+0 sets of disks and then stripe across them using

> Veritas Volume Manager. Each set of 4+4 disks would be one LUN. In this

> case, for every 1 "disk" (LUN) that the OS sees, there would actually be

> 8 physical disks (4-disk wide stripe, mirrored). For example, if I'm

> using VxVM to stripe across 4 "disks" (actually LUNs), there would

> actually be 32 physical disks (16 disk stripe mirrored to another 16

disks).


>

> My confusion is with the recommended 1 MB stripe depth. From what I've

> read, 1 MB was chosen because if a disk is writing 1 MB of data at a

> time, only one seek is required for that write size. 1 MB per seek can

> considered a sequential write and is more efficient. Anything larger

> than 1 MB barely increases the efficiency.

>

> So, is the 1 MB stripe depth at the Volume Manager level or at the

> physical disk level? Here's why I ask:

>

> If I do an 8 disk RAID 1+0 (4 disk stripe, mirrored) on my hardware RAID

> array and present that as a single LUN to my server, a 1 MB write to

> that LUN will result in 256KB written to each physical disk (if I'm

> striping evenly across the disks for that I/O size). A 256KB write to

> the physical disk is less efficient than the 1 MB write that all the

> SAME whitepapers I've read talk about. On the other hand, if I stripe at

> the hardware level with a 1 MB stripe depth across 4 disks, that results

> in a 4 MB stripe depth at the VxVM level to maintain the efficency.

> Neither of those choices seems quite right.

>

> Does anyone else have a similar SAME/Oracle/hardware RAID situation?

> What have you done and how has it worked out?

>

> I'm really not interested in a religious debate about the the merits (or

> lack thereof) of the SAME methodology. I'm just looking for people who

> have done something similar to what I've described.

>

> The reason I would go with the 4-disk wide stripe (8-disk RAID 1+0) is

> to simplify adding disks in the future. I would  add disks one 4x4 set

> at a time and then do a background relayout at the VxVM level to

> maintain the SAME principle. The 8-disk (4x4) increment would be simpler

> and less expensive that going with a 16-disk (8x8) increment.

>

> Finally, should this whole set of disks be one gigantic volume or should

> I have a datafile volume, a redo volume, and index volume, etc? Separate

> volumes would be better from an organizational/administrative point of

> view, but what about performance? Having everything on separate volumes

> would guarantee longer seek times as the heads move between volumes on

> these super-wide stripes. In the long run, I suspect that it really

> won't matter much.

>

> It shouldn't matter, but this if for a multi-terabyte data warehouse

> that is receiving large amounts of new data hourly as well as crunching

> what is already in there.

>

> Thanks for the patience it took to get this far.

>

> Ron

>