Comments on: RAID on RAID - plaiding http://storageadvisors.adaptec.com/2006/12/18/raid-on-raid-plaiding/ Storage Solutions for Real World IT Professionals Sat, 20 Mar 2010 08:22:33 +0000 http://wordpress.org/?v=1.5.2 Comment on RAID on RAID - plaiding by: Oz Mundim http://storageadvisors.adaptec.com/2006/12/18/raid-on-raid-plaiding/#comment-62522 Wed, 27 Jun 2007 13:45:43 +0000 http://storageadvisors.adaptec.com/2006/12/18/raid-on-raid-plaiding/#comment-62522 I needed some advice. Very nice discussion, by the way. Wondering big, let's say I have a server controlling RAID 5 of 3 iSCSI disk array which are also set to RAID 5. Now I wanted to install iSCSI target on that 'RAID controller' server and share the md volume to 10 nodes (acting in cluster with clvm and GFS) via iSCSI. Here's the scenario: 10 nodes (cluster) ----- iSCSI initiator -----> (iSCSI Target) RAID controller box (RAID 5) ------ iSCSI Initiator ------> 3 iSCSI Disk Array Would performance be to bad to make this setup impossible to accomplish? Unless is too bad, I'm not concerned about performance. High availability and fast storage growing are my goal. Network would be handled by Cisco 4503 Gigabit switches. Oz I needed some advice. Very nice discussion, by the way.

Wondering big, let’s say I have a server controlling RAID 5 of 3 iSCSI disk array which are also set to RAID 5.

Now I wanted to install iSCSI target on that ‘RAID controller’ server and share the md volume to 10 nodes (acting in cluster with clvm and GFS) via iSCSI.

Here’s the scenario:

10 nodes (cluster) —– iSCSI initiator —–> (iSCSI Target) RAID controller box (RAID 5) —— iSCSI Initiator ——> 3 iSCSI Disk Array

Would performance be to bad to make this setup impossible to accomplish? Unless is too bad, I’m not concerned about performance. High availability and fast storage growing are my goal.

Network would be handled by Cisco 4503 Gigabit switches.

Oz

]]> Comment on RAID on RAID - plaiding by: Steve http://storageadvisors.adaptec.com/2006/12/18/raid-on-raid-plaiding/#comment-24808 Tue, 02 Jan 2007 16:46:23 +0000 http://storageadvisors.adaptec.com/2006/12/18/raid-on-raid-plaiding/#comment-24808 the open source community has a linux iSCIS target project - it can be found at: http://iscsitarget.sourceforge.net/ I would not recommend RAID 0 at the host, as data corruption is certain if any of the iSCSI targets go off line. remember, RAID 0 your data is stripped across each segment, loss of any one segment(for any reason) you lose all the data. I also tried building a RAID 5 at the host with three LUNs from a single target, it seemed to take forever to sync even a fairly small RAID set. you should experiment with degraded and resync scenarios, if you think you want to have RAID 5 at the host. I recommend RAID 1 at the host, as it is very low overhead on the host system; then you can use RAID 5 or 6 at the targets. again, RAID 1 at the host is for redundancy. alternatively, you can go RAID 0 at the target; this should be the fastest config and you have a complete mirror with the second iSCSI target. SR the open source community has a linux iSCIS target project -
it can be found at: http://iscsitarget.sourceforge.net/

I would not recommend RAID 0 at the host, as data corruption is certain if any of the iSCSI targets go off line. remember, RAID 0 your data is stripped across each segment, loss of any one segment(for any reason) you lose all the data.

I also tried building a RAID 5 at the host with three LUNs from a single target, it seemed to take forever to sync even a fairly small RAID set. you should experiment with degraded and resync scenarios, if you think you want to have RAID 5 at the host.

I recommend RAID 1 at the host, as it is very low overhead on the host system; then you can use RAID 5 or 6 at the targets.
again, RAID 1 at the host is for redundancy. alternatively, you can go RAID 0 at the target; this should be the fastest config and you have a complete mirror with the second iSCSI target.

SR

]]> Comment on RAID on RAID - plaiding by: Mark http://storageadvisors.adaptec.com/2006/12/18/raid-on-raid-plaiding/#comment-22748 Tue, 19 Dec 2006 02:07:48 +0000 http://storageadvisors.adaptec.com/2006/12/18/raid-on-raid-plaiding/#comment-22748 forgot the other main question... If I go RAID6 on the storage node/subsystems, and RAID0 across my volume manager... What happens if I lose a disk? That was the root question I had :) This makes growing the volumes on the management server easier. If I have to RAID5 in BOTH places, then its probably not worth the cost in extra hardware. forgot the other main question…

If I go RAID6 on the storage node/subsystems, and RAID0 across my volume manager… What happens if I lose a disk? That was the root question I had :)

This makes growing the volumes on the management server easier. If I have to RAID5 in BOTH places, then its probably not worth the cost in extra hardware.

]]> Comment on RAID on RAID - plaiding by: Mark http://storageadvisors.adaptec.com/2006/12/18/raid-on-raid-plaiding/#comment-22747 Tue, 19 Dec 2006 02:03:44 +0000 http://storageadvisors.adaptec.com/2006/12/18/raid-on-raid-plaiding/#comment-22747 Thanks for the response Steve. This is for an easy to expand archiving system. Performance does not matter, but ability to expand in to potential PB does. Given the backplane on a good quality 48 port GB switch with fiber uplinks to the Volume management server (Veritas or the like). This is all Linux based, likely something like Ent. ISCSI Target Project, or better yet hopefully REHL or SUSE will support a target soon! (do they now??) The storage nodes running raid5 or 6 would be done for easy / cheap expansion (cheap 750 or 500gb sata), and the volume manager would make it simple and easy to expand, and give the ability to export large volumes in nfs or iscsi easily. Need more storage, just build up another storage node with internal RAID, and grow your software volume on the management server... Is it as easy and cheap as it sounds? (when performance is not a concern) Thanks again! Thanks for the response Steve. This is for an easy to expand archiving system. Performance does not matter, but ability to expand in to potential PB does. Given the backplane on a good quality 48 port GB switch with fiber uplinks to the Volume management server (Veritas or the like). This is all Linux based, likely something like Ent. ISCSI Target Project, or better yet hopefully REHL or SUSE will support a target soon! (do they now??)

The storage nodes running raid5 or 6 would be done for easy / cheap expansion (cheap 750 or 500gb sata), and the volume manager would make it simple and easy to expand, and give the ability to export large volumes in nfs or iscsi easily.

Need more storage, just build up another storage node with internal RAID, and grow your software volume on the management server… Is it as easy and cheap as it sounds? (when performance is not a concern)

Thanks again!

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