We've had large ext3 filesystems go readonly (underlying hardware problem) and recovery can take a days. For this I'm using ext3 as well and as it's a raid 6 disk (hardware raided) I can probably get away with 4X1TB. But I'm currently experiencing bad performance on a single brick that's not mirrored..... ________________________________ From: Mark Mielke [mailto:mark at mark.mielke.cc] Sent: 12 August 2009 18:51 To: Hiren Joshi Cc: gluster-users at gluster.org Subject: Re: Performance On 08/12/2009 01:24 PM, Hiren Joshi wrote: 36 partitions on each server - the word "partition" is ambiguous. Are they 36 separate drives? Or multiple partitions on the same drive. If multiple partitions on the same drive, this would be a bad idea, as it would require the disk head to move back and forth between the partitions, significantly increasing the latency, and therefore significantly reducing the performance. If each partition is on its own drive, you still won't see benefit unless you have many clients concurrently changing many different files. In your above case, it's touching a single file in sequence, and having a cluster is costing you rather than benefitting you. We went with 36 partitions (on a single raid 6 drive) incase we got file system corruption, it would take less time to fsck a 100G partition than a 3.6TB one. Would a 3.6TB single disk be better? Putting 3.6 TB on a single disk sounds like a lot of eggs in one basket. :-) If you are worried about fsck, I would definitely do as the other poster suggested and use a journalled file system. This nearly eliminates the fsck time for most situations. This would be whether using 100G partitions or using 3.6T partitions. In fact, there is very few reasons not to use a journalled file system these days. As for how to deal with data on this partition - the file system is going to have a better chance of placing files close to each other, than setting up 36 partitions and having Gluster scatter the files across all of them based on a hash. Personally, I would choose 4 x 1 Tbyte drives over 1 x 3.6 Tbyte drive, as this nearly quadruples my bandwidth and for highly concurrent loads, nearly divides by four the average latency to access files. But, if you already have the 3.6 Tbyte drive, I think the only performance-friendly use would be to partition it based upon access requirements, rather than a hash (random). That is, files that are accessed frequently should be clustered together at the front of a disk, files accessed less frequently could be in the middle, and files accessed infrequently could be at the end. This would be a three partition disk. Gluster does not have a file system that does this automatically (that I can tell), so it would probably require a software solution on your end. For example, I believe dovecot (IMAP server) allows an "alternative storage" location to be defined, so that infrequently read files can be moved to another disk, and it knows to check the primary storage first, and fall back to the alternative storage after. It you can't break up your storage by access patterns, then I think a 3.6 Tbyte file system might still be the next best option - it's still better than 36 partitions. But, make sure you have a good file system on it, that scales well to this size. Cheers, mark -- Mark Mielke <mark at mielke.cc> <mailto:mark at mielke.cc>
